Contextual Factors and Programme Theories Associated with Implementing Blue Prescription Programmes: A Systematic Realist Review

adequate to strong quality were included from 8,619 records. After participating in BPPs referred to or prescribed by health and social care professionals, service users had improvements in their physical, cognitive (mental), social health, and pro-environmental knowledge. Service user-related contextual factors were referral information, free equipment, transportation, social support, blue space environments, and skills of service providers. Programme-related contextual factors were communication, multistakeholder collaboration, fnancing, and adequate service providers. Programme theories on service user enrolment, engagement, adherence, communication protocols, and programme sustainability explain the mechanisms of BPP implementation. BPPs could promote health and wellbeing if contextual factors and programme theories associated with service users’ characteristics and programme delivery are considered in the design, delivery, and evaluation of BPPs. Our study was registered with PROSPERO (CRD42020170660).

Consequently, social prescribing (SP), an umbrella term for health and social care interventions that promote health and wellbeing by connecting individuals to nonmedical and community-based interventions [8], utilised the healthpromoting benefts of nature [9] to deliver nature-based social prescribing (NBSP) [10].Moreover, NBSP, especially those that use blue space activities, could be considered a personal feedback action based on the Blue Space and Health/Wellbeing Model [1].SP is usually delivered using signposting, direct referral, link worker, or holistic link worker pathways, typically initiated by healthcare professionals (i.e., general practitioner/GP) [11].SP implementation could also be described by programme theories on patient enrolment (frst successful referral), engagement (attendance to frst session), and adherence (maintained participation over time) [11][12][13].Tere are also suggestions that successful referral uptake and sustainable SP implementation require link workers who facilitate the delivery of social prescriptions and liaise with health and social care facilities and third sector organisation, as well as fnancial and partnership support [11,[14][15][16].
SP could help motivate individuals engage with healthpromoting behaviours (e.g., physical activity and socialisation) [14,16].Findings from a meta-synthesis of evidence suggested that SP improved individuals' sense of belongingness, self-confdence, and sense of purpose, thereby, decreasing feelings of loneliness and isolation [17,18].Another systematic review suggested that SP could improve prosocial behaviours, specifcally in forging social networks and cohesion through the social cure process, aside from physical and mental wellbeing [19,20].Additionally, SP could alleviate the healthcare burden by depressurising the healthcare workload and decreasing healthcare usage [14,20].A nationwide SP programme in the UK proved that the intervention had good value for money indicating a social return of £3.42 for every £1 investment in the service [21].
Furthermore, NBSP or nature prescription delivers the health-promoting benefts of nature by referring individuals to activities that connect them with nature [9,10].Until recently, nature prescription was called green prescription, characterised by connecting people to green spaces (e.g., parks, forests).NBSP delivers environmental, economic, and social co-benefts [22].A systematic review suggested that NBSP is a low-cost intervention promoting prosocial (e.g., social connectedness) and proenvironmental behaviours (e.g., conservation volunteering) by providing opportunities for social and nature connections simultaneously [10,23,24].Tere is much evidence on the health benefts of nature exposure conducted prior to the COVID-19 pandemic, and research during the pandemic also suggested similar benefts.An increase in health-related use of blue/ green spaces during lockdowns suggested that these spaces helped people cope with mental health stressors [25][26][27].Populations sampled in the UK and Spain associated exposure to nature with mental health improvements and better sleep quality during the COVID-19 pandemic [28,29]; and fewer mental and physical symptoms suggest a bufering efect on the impacts of isolation [30][31][32][33].Large proportions of blue/green spaces were also attributed to lower COVID-19-related cases and deaths in Poland [34].
Despite robust evidence on the general, physical, and mental health benefts of contact with blue spaces [1,31,35,36], many implementation models of NBSP overlooked the health-promoting benefts of blue spaces (e.g., lakes, rivers, seas, wetlands, canals, etc.).Systematic reviews on NBSP focused on the health outcomes of using green spaces [37].In Scotland, the Green Health Partnership focused on green space activities (e.g., park runs and forest walks) for obesity prevention, mental health promotion, and the improvement of public health [38].Moreover, the implementation and evaluation of SP have several contextual barriers which could be extended to NBSP.An implementation model that considers the suitability of social activities with service users, referral pathways, skills of 2 Health & Social Care in the Community human resource, fnancing mechanisms, stakeholder partnerships, comparable outcome measures, evaluation frameworks, and contextual factors that infuence uptake of service users is needed [11,15,16,[39][40][41][42][43].
To our knowledge, these evidence gaps have not been investigated for NBSP that uses blue spaces (or blue prescription programme/BPP).One systematic review highlighted barriers in implementing blue space activities (e.g., accessibility, equipment, and training of service providers) [44]; however, there is no model describing the mechanisms of BPP implementation.Hence, we conducted a systematic realist review to investigate the health benefts, service user suitability, referral pathways, and contextual factors associated with BPP implementation to inform the development of programme theories and a logic model that would explain the mechanisms of programme implementation.

Methods
A systematic realist review investigates why interventions work in certain circumstances by interrogating contexts, mechanisms, and outcomes of programme implementation [12].We followed Berg's [45] steps for conducting realist reviews.

Question Identifcation and Purpose of Review.
We defned BPP as individual or group activities that take place in or around blue spaces or natural water environments (e.g., surfng, swimming, kayaking, etc.) (interventions), which were referred to or prescribed by health and social care professionals (e.g., GPs, pharmacists, social workers, etc.) (population) using the four SP referral pathways and with health-and wellbeing-related outcomes.Our setting (context) was health and social care facilities where many individuals are referred to or prescribed with health and social care interventions.We included case reports, qualitative, case-control, cohort, pre-post intervention studies, nonrandomised, and randomised controlled trials published in English.We limited the publication period from January 2000 to June 2022 as research on the health-blue space nexus emerged in the early 2000s [36,44].We excluded studies where activities were not conducted in natural water environments and were referred/prescribed by nonhealth or nonsocial care workers through advertisements and recruitments.

Articulating Initial Programme
Teories.Programme theories (PTs) (e.g., logic models or if-then statements) are analytical units in realist reviews that suggest "contextmechanism-outcome" relationships to describe how interventions work [12,13,46,47].PTs inform the development of logic models used in planning, designing, and evaluating complex interventions [48].Logic models are composed of inputs, activities, outputs, and outcomes [49].We used the following PTs on SP based on literature and analysed if these are true to BPP implementation models by investigating their occurrence in the included studies.Based on this, we redeveloped the initial PTs to form the fnal PTs that could best explain BPP implementation.

Initial PT1 (Patient Enrolment).
If the referral is presented in an acceptable manner, it is compatible with the patient's needs and expectations, and the patient believes that it will improve their condition, then they may enrol [11].

Initial PT2 (Patient Engagement
).If transportation is provided making the socially prescribed activity accessible to the patient, then they will engage [11].

Initial PT3 (Patient Adherence
).If the service providers are skilled and there are improvements on patient's condition, then they are more likely to keep attending [11].

Initial PT4 (Link Worker Coordination).
If there are link workers facilitating the delivery of social prescriptions and liaising with health and social care facilities and third sector organisations, then the referral uptake will be successful [11,[14][15][16].

Initial PT5 (Partnership with Community-Based Organisations).
If the partnership between health and social care facilities and community-based organisations is fnancially supported, then the delivery of social prescribing programmes will be sustained [14][15][16].

2.3.
Searching and Appraising Evidence.We followed the PRISMA guidelines for record screening [50].We searched PubMed, Web of Science, PsycINFO, MEDLINE, Scopus, and CINAHL using keyword strings (Table 1) and conducted a snowball search by screening reference lists of systematic reviews collected from database searches [51,52].Records were uploaded, deduplicated, and screened using Rayyan QCRI [53].Title and abstract screening were conducted by: JA, KH, SCh, MG, PK, ZT, NS, YYC, FCO, AE, ES, and 13 volunteer researchers of the Blue-Green Prescribing Reviewers Group.Full-text screening were independently conducted in pairs by: JA-KH, JA-SCh, JA-ES.KNI resolved conficting decisions.
2.5.Synthesising Findings.We employed realist synthesis to analyse and synthesise extracted data [12,13].JA used hybrid coding in NVivo 12 [57] to develop themes of contextual factors (CFs) associated with BPP implementation from the extracted data.JA mapped out the existence of developed CFs in the collected evidence to associate these with the initial PTs.Te association of CFs and initial PTs informed the redevelopment of the initial PTs to establish the fnal PTs (i.e., "if-then" statements) explaining BPP implementation [12,13,46,47].CFs and fnal PTs were refned by JA during consultations with co-authors, specifcally KH, KNI, and SCh, members of the research advisory team (RH, SP, and SCu), and other stakeholders from the Hydro Nation Steering Group.We then developed an overall BPP logic model based on the CFs and fnal PTs [48,49].
Our study was registered with PROSPERO (CRD42020170660).

3.1.
Search.We collected 8,619 records from combined sources (Figure 1).Te 4,532 duplicates and 3,917 irrelevant reports were excluded during the title and abstract screening.Te 167 and 288 reports were further excluded at full-text screening.Sixteen studies were included in the review.
3.2.Quality Assessment.Quality assessment results are reported in Table 2.
Seven qualitative studies had adequate quality [59-65] and were downgraded due to limitations in study design, sampling strategy, data collection, analysis, presenting conclusions, verifcation, and refexivity procedures.

Characteristics of Included Studies.
Extracted data were tabulated according to inputs (facilities, health and social care professionals, duration, and timescale), activities (referral pathway, overall programme format, and blue space activity), and health outcomes.Tis aided the development of the fnal PTs and the logic model.We also extracted data on service user characteristics and their health status (Table 3).

Service Users, Referral Pathways, and Health Outcomes of
BPPs in Social Care Facilities.Five studies were in social care institutions, foster or residential care homes for young people, and community wellbeing centres [62,63,67,68,71].Young people and adults with mobility and sensory impairments and who were at higher risk to psychosocial problems, anxiety, and depression were directly referred to surfng by either a team of a social or residential care worker and therapist [62]; social workers and adolescent educators [67]; residential care worker [71] or a social child support specialist [62,67,68].Adults and elderly service users who had anxiety and depression were referred to guided river walks, bird/otter watching, and canoeing by mental health workers through a link worker [63].Service users experienced improved daily functioning [68]; ftness and physical activity [67,68]; mental and emotional wellbeing [67,68,71] self-esteem [68], interpersonal competencies and prosocial behaviour [62,67,68,71] proenvironmental knowledge; and nature 6 Health & Social Care in the Community connection [62,63].Some reported health outcomes showed no signifcant efects on depression, anxiety, selfesteem, emotion regulation, social connectedness, sleep quality, and physical activity [71].
Te association and coexistence of CFs and initial PTs in each study informed the redevelopment of initial PTs to articulate the fnal PTs that could best explain BPP implementation (Table 5).Final PTs on service user enrolment (PT1), engagement (PT2), adherence (PT3), communication protocols (PT4), and long-term programme sustainability (PT5) could best explain BPP implementation.We redeveloped these fnal PTs with the assumption that individuals with physical and/or mental health conditions sought health and social care service in health, social care, or specialised educational facility, eventually enrolling in and engaging with BPPs.

Final PT1: If Service Users' Apprehensions and Optimistic Expectations are Positively Infuenced by Information on BPPs
Provided by Prescribers, Ten Tey May Enrol.Te fnal PT1 does not difer from the initial PT1 [11], especially on the provision of acceptable and compatible referral information.
However, our study identifes that there is a need to resolve service users' apprehensions towards BPPs by presenting positive information about the intervention.Some service users were optimistic regarding BPPs, but others had apprehensions, fear, and anxiety [62,73] due to its novelty, unfamiliar environments, and lack of experience.Knowledge sharing about the type, structure, and benefts of BPPs, coupled with maps, pedometers, and activity guides informed service users' decision to enrol [70,72].Tis information was further reinforced by written prescriptions and link worker communication [70].However, some healthcare workers raised concerns about the time requirement for flling out paper prescriptions and providing counselling.It was suggested that blue prescriptions could be integrated into an electronic prescribing system [70].Information on programme structure is important for service users since some are delivered as structured [59,63,67,70,71,73,74] or unstructured programmes [64,70,72].Having a predictable and structured programme of activities was found suitable for service users who experienced stressful and unpredictable events [71].Information on logistics was useful since some were stay-in activities requiring meals and lodging [59,60,64,69,74], although some were stay-out [61-63, 65, 68, 70, 72, 73].

Final PT2: If Service Users Are Provided with Free Logistics, Equipment, and Transportation to Access a Socially Supportive and Client-Centred Blue Space Activity and Environment,
Ten Tey May Engage.Similar to initial PT2 [11], fnal PT2 highlights the importance of transportation to help service users access and eventually, engage with BPPs.Additional contextual factors infuencing service user engagement include programme compatibility with service users, other determinants of accessibility (e.g., provision of equipment, food, and accommodation), and the social and blue space environments.Service user engagement was associated with their preference, skills, and psychosocial fulflment [68,69].Consulting people with disabilities on how to make the design of assistive infrastructures more accessible, compatible, and adaptive to their needs facilitated engagement of service users [59,62].Service users had a strong interest in BPPs because these were free [70]; however, some required costly equipment (e.g., surfboards, canoes, and kayaks).Providing equipment, transportation, and camping fees encouraged engagement especially for activities in distant locations [59, 63, 68, 70−74].Travelling in groups facilitated socialisation that relieved anxious participants [63].Wildlife and blue space environments facilitated relaxing experiences, distraction, engagement of human senses, self-strength, and acclimatisation [59,60,63,65,71,74].Weather and sea conditions were uncontrolled efect modifers that impacted engagement [1,69,71].

Final PT3: If Service Users Experience Social Support and Health Improvement through Blue Space Activities Delivered by Knowledgeable and Skilled Service Providers, Ten Tey
May Adhere.Te fnal PT3 is similar to the initial PT3 [11] on the infuence of skilled service providers and health Health & Social Care in the Community improvement on service user adherence.Skilled service providers ensured standardised programme delivery through regularly evaluated guidelines [69].Some service providers were trained in working with service users who have disabilities (i.e., proper use and introduction of surfng boards for children with ASD) [62,66].Our study added that the values of service providers and social support provided to service users infuence their adherence.Positive values of service providers were appreciated by the service users [59,62,63,65,69,72,73].Te encouragement, enthusiasm, and positive motivation through constructive observations created a friendly atmosphere and empowered service users to explore new activities [62, 63, 65, 71−73].Staf responsiveness facilitated connections with service users [64,75] through open communications [71,72].Tis was perceived as genuine care and willingness to help [73].Improvements in physical, cognitive (mental), social health, and proenvironmental knowledge were also associated with service user's adherence [60-63, 65-69, 71−74].

Final PT4: If Communication Protocols Are in Place between Service Users, Prescribers, Link Workers, and Service Providers, Ten BPPs May Be More Visible and Successfully
Implemented in Health and Social Care Facilities.Final PT4 highlights the importance of communication protocols between service users, prescribers, service providers, and carers as tools for programme coordination, making BPPs visible in health and social care facilities [73,71].Initial presentation of BPPs to prescribers facilitated planning of referral processes, requirements, and responsibilities [67,70].Electronic communications between prescribers and service providers served as feedback channels to discuss service users' health conditions [70].BPP champions acted as programme leads and maintained coordination and programme visibility in health and social care facilities [70].Some link workers facilitated inclusive communication between prescribers, service users, and service providers by using preferred and appropriate media (e.g., telephone, emails, text messaging) [64,70,72].Communications between service users and their carers were opportunities for awareness raising and socialisation [62].In-and out-group socialisation through interest-based grouping and matching contributed to self-improvement, confdence, and improved communication skills [62, 64, 67, 70−73].
3.12.Final PT5: If BPPs Receive Organisational, Stakeholder, Funding, and Policy Support, Ten Tese Are More Likely to Be Sustainably Implemented.Final PT5 highlights the importance of organisational (e.g., staf, volunteer), stakeholder, fnancial, and policy support on programme sustainability.Surf therapy was perceived as benefcial by health sector stakeholders, practitioners, general public, and policymakers because the cost (£50/session) was less than the mental healthcare cost (£265/year) for children [62,67,69,71,75].However, this economic evaluation was not robust and requires further appropriate assessment [67].Some BPPs were created through health and third sector partnerships facilitating shared resources and fnancial support that covered implementation requirements (e.g., meals, transportation, and equipment) [59,60,62,[68][69][70].Adequate skilled staf and volunteers were the backbone of BPPs.Te service provider to service user ratio depended on participant intake, type of activities, and fnancial capacity [63,[66][67][68]70].Depending on activities, resources (e.g., fnances, equipment, volunteers, and staf), and the number of service users, some BPPs were delivered in 2 : 1 service   Health & Social Care in the Community  Health & Social Care in the Community Health & Social Care in the Community  Initial PT1: if a referral is presented in an acceptable manner, it is compatible with the patient's needs and expectations, and the patient believes that it will improve their condition, then they may enrol (enrolment) [10].Initial PT2: if transportation is provided making the socially prescribed activity accessible to the patient, then they will engage (engagement) [10].Initial PT3: if the service providers are skilled and there are improvements on patient's condition, then they are more likely to keep attending (adherence) [10].Initial PT4: if there are link workers facilitating the delivery of social prescriptions and liaising with health and social care facilities and third sector organisations, then the referral uptake will be successful (link worker coordination) [10,[13][14][15].Initial PT5: if partnership between health and social care facilities and community-based organisations is fnancially supported, then the delivery of social prescribing programmes will be sustained (partnership with community-based organisations) [13][14][15].14 Health & Social Care in the Community  If the partnership between health and social care facilities and community-based organisations is fnancially supported, then the delivery of social prescribing programmes will be sustained [14][15][16] People with physical and/or mental health conditions seek health and social care (some were accompanied by their carers) Health or social care facilities and community-based organisations CF18 organisational support (staf and volunteers) CF19 stakeholder support CF20 funding and policy support Final PT5: long-term programme sustainability of blue prescription programmes (long-term programme sustainability) If BPPs receive organisational, stakeholder, funding, and policy support, then these are more likely to be sustainably implemented 16 Health & Social Care in the Community provider to service user ratio [66], whilst others were in 1 : 1, 1 : 2, or 1 : 3 ratios [67,68,71].
Te logic model explains the mechanisms of BPPs implementation in health, social care, and specialised educational facilities (Figure 2).Tis logic model is informed by data on inputs (e.g., natural resources, physical, human resources, intellectual, and fnancial); service user-(e.g., enrolment, engagement, and adherence) and programmerelated (e.g., communications and sustainability) activities; outputs; intermediate health outcomes (e.g., physical, cognitive/mental, social, and environmental); and health and wellbeing impacts.We assumed that individuals with physical and/or mental health conditions seek health and social care in either health, social care, or specialised educational facilities.

Discussion
BPPs implemented in health and social care facilities had benefts on the general, physical, cognitive (mental), and social health and proenvironmental knowledge of service users.We present a synthesised logic model that demonstrates the holistic implementation of BPPs.Te mechanisms of BPP implementation are explained by PTs on service user enrolment, engagement, adherence, communication protocols, and long-term programme sustainability and are associated with CFs on service user's needs and characteristics; accessibility; compatibility; social and blue space environments; skills and values of service providers; health improvement; communication; multistakeholder partnership; fnancing; and policy.
Our review is consistent with existing evidence demonstrating the health and wellbeing benefts of contact with blue spaces [1,36,76] and participation in NBSP [11,37].Our study is also consistent with the evidence that contact with nature (i.e., blue spaces) through NBSP could improve proenvironmental knowledge and prosocial behaviours [10, 22, 77−79].Investigated BPPs were combinations of water-based and psychoeducational activities which could explain improvements in service users' proenvironmental knowledge about the value of blue spaces.Tese also provided venues for interpersonal opportunities characterised as safe spaces for social interactions highlighting that "sociability" in NBSP harnesses service user's social skills as they interact with places, social settings, and shared stories [80].Te existence of communication protocols might have also reinforced interactions between service users and providers.
Young people and veterans who were at high-risk or experienced mental health conditions (e.g., anxiety, depression, PTSD, etc.) were predominantly referred to or prescribed with blue space activities (e.g., therapeutic fyfshing and surf therapy).In contrast to another study [44], we did not include research involving women with breast cancer who participated in dragon boating because there was no sufcient information that this was prescribed using SP referral pathways.Te large number of young people referred to BPPs could be an opportunity for BPPs to be used as a tool to promote childhood nature experience and improve proenvironmental behaviours [81].However, it is important to note that prescribing time in nature could be perceived as a medical order rather than a personal choice [82], which could compromise engagement and adherence, especially for younger participants.Extrinsic motivation (i.e., prescribing specifc blue space environments and activities) could impact service users' intrinsic motivation to visit nature, compromising its health benefts [82].Sockhill et al. [83] suggested that behavioural interventions should be tailor-ftted to the values and degree of an individual's connection with nature in order to maximise the generation of proenvironmental behaviours.Te design and delivery of BPPs should be based on the needs, environment, and personal circumstances of the service users.
Written prescriptions could facilitate enrolment of service users because these were perceived as an alternative to pharmaceutical prescriptions [38,84].Te provision of positive information using appropriate consultation and motivational techniques could reinforce service users' agency and motivation to enrol in and engage with BPPs.Service user-centred approaches could facilitate their autonomy since this is an opportunity to understand the compatibility of BPPs with the service users' health and personal needs [85][86][87][88].Investigated blue space activities had a higher duration than the 120 minutes per week recommended dose of nature [89].Time or duration is a personal efect modifer for blue space engagement [1].Tus, programme duration should be matched with service users' gender, age, ethnicity, and health conditions [90][91][92][93][94][95][96][97][98][99] because diferent individuals may be in situations that could limit their engagement.Reducing session time might also promote engagement amongst the elderly population [100].Increasing choices for blue space activities such as dragon boating [44], recreational diving [101], open water swimming [102,103], and cycling near blue spaces [104][105][106] could also increase the compatibility to individuals with varying preferences.Providing service users with variable and fxed noncash incentives (e.g.transportation, food, accommodation, and health benefts) may improve enrolment and engagement and could improve proenvironmental behaviours [107].
Accessibility also infuences service users' engagement and adherence to NBSP [11].However, closer proximity to blue spaces is not always associated with better mental health [108], suggesting that proximity to blue spaces might not always translate to BPP adherence.Our review suggests that BPPs package the health-promoting benefts of blue spaces into structured interventions making blue spaces more accessible to those who could most beneft from these.Nevertheless, accessibility should be an important consideration for prescribers and service providers in designing and delivering BPPs.From a behaviour change perspective [109], improving the quality and accessibility of blue spaces could provide greater opportunities for exposure with these [1].Equipment; adaptive infrastructure for people living with disability; accommodation; and meal requirements infuence accessibility.Programme adaptation is important for service users who have fears or discomfort in blue spaces.A gentle, intuitive, and encouraging approach is Health & Social Care in the Community recommended to participants with serious mental health conditions to avoid retraumatisation [100].Adaptation should be coupled with capability-building (e.g., knowledge sharing) and motivational strategies (e.g., social support), through referral, prescription, or motivational counselling, helping to promote and sustain contact with natural settings [110].
Reviews on SP and green prescription models highlighted the doctor-patient relationship, capacity of service providers, and supportive social environments as factors associated with participant uptake [11,37,38].Tese were highlighted in our review in addition to communication protocols, stakeholder collaboration, and policy support.Engagement with and adherence to BPPs were facilitated by positive healthcare worker and service user interactions because it promotes selfconfdence, motivation, and optimism amongst service users [111].However, our review suggests that blue space activities are prescribed by either healthcare/social care workers/educators with diferent specialisations.Tis underscores the multistakeholder nature of NBSP where BPPs could be delivered by the broader health and allied professions [44].Healthcare providers have a high interest in nature prescriptions, but many remain untapped due to limited awareness and time.Similar to Besenyi et al. [112], our review highlights the limited time of healthcare providers in prescribing BPPs.Tis could be resolved by integrating link workers responsible for virtual/in-person motivational interviews and coordination of BPP referrals with third sector providers [112,113].Link workers' roles are recognised in the UK's National Health Service [114] because they support healthcare delivery by helping service users fnd health solutions [11,[14][15][16].However, standardised training on delivery protocols, especially in managing the social and environmental risks associated with blue space activities is needed [115].
Recent COVID-19 pandemic lockdowns magnifed nature's health-promoting benefts [116].NBSPs were provided virtually through telephone or video referrals and virtual health walks during lockdowns [117].NBSPs such as BPPs could alleviate the social and economic pressures of the COVID-19 pandemic [118] if used as a complementary service for mental healthcare.However, a siloed approach in tackling the mental health epidemic compounded by limited resources could hinder efective implementation.Before the COVID-19 pandemic, some NBSPs were discontinued due to cost, capacity, limited information, lack of transportation, and communication [116,117,119].A critical systems thinking approach could be used in designing, implementing, and evaluating BPPs to ensure that implementation models holistically consider issues on human resource, technology and logistical requirements, quality assurance, sustainability, and collaboration between stakeholders for resource and knowledge sharing and successful buy-in [40].Tese collaborations and resources should address identifed contextual factors infuencing enrolment, engagement, and adherence of service users alongside efective communication and programme sustainability.
Many BPPs are formed through stakeholder partnerships which are funding dependent.Unstable funding impacts programme sustainability [14] compounded by concerns on the capacity and readiness of service providers due to the increasing demand to outdoor water-based activities [115].Policies on institutionalising BPPs in government-funded health services to funnel resources and build stakeholder capacities are necessary.However, the cost beneft of health interventions is a concern for policymakers before investing.Living near blue spaces [120] and providing BPPs have associations with reduced antidepressant prescription, suggesting its potential  contribution to decreasing antidepressant spending.Moreover, initial insights into the economic returns of investing in NBSP suggest that the 10-year total beneft to cost ratio ranges between 7.61 and 27.1 [118].However, there are questions on more appropriate social, economic, and environmental evaluations [115,121] for BPPs due to their diferent spending requirements for equipment, programme delivery, and environmental setting.Lastly, even though BPPs could have positive impacts on the health and value of nature [100], medicalising the ecosystem services of blue spaces could go against some ecological paradigms [122].Blue space activities could cause disturbances to wildlife, human-induced pollution, and other irreversible environmental degradation [123][124][125][126]. Te ethical principles of benefcence and nonmalefcence [85] should be applied in designing, delivering, and evaluating human and planet-centred BPPs by involving health, environmental, and community-based stakeholders.

Strengths and Limitations
We ofer robustly developed CFs, PTs, and a logic model for the development, implementation, and evaluation of BPPs.However, our review has some limitations.Our search included a broad range of keywords on blue spaces, but its combination with other keywords (i.e., "prescription") may have limited the hits for articles that did not use these keyword combinations.Some studies did not specify the presence of blue spaces in their interventions, especially those that referred to blue spaces as components of green spaces due to ambiguities on defnitions in the literature.Tis made it difcult to identify studies that only used blue spaces.Tus, we did not include studies with unclear information on the use of blue spaces and referral pathways.We did not include grey literature, which could provide more information about CFs and mechanisms of BPP implementation.Tere were limitations on the quality of individual studies specifcally for controlling confounders, reporting variance estimates, strategies for data collection, verifcation, and refexivity.Realist review is also subjective [37], especially in interpreting how CFs inform PTs.We interrogated our results during consultative meetings with a set of transdisciplinary stakeholders to avoid potential interpretation bias.Geographical homogeneity was a limitation.Some studies had participants from diferent ethnicities and sociodemographic backgrounds, but all studies were conducted in Global North countries, which could mean missing out on contexts of programme implementation in the Global South.

Research Directions
We suggest employing intervention studies examining the impacts of BPPs on physical and mental health with appropriate and robust health, economic, and social evaluation techniques.Implementation research and pilot studies based on strongly developed logic models are needed to establish a "proof of concept" that is viable for real-world implementation, scaling up, and institutionalisation. Te causation and long-term implications of BPPs on population health, healthcare service delivery, and the environment should also be investigated.

Conclusion
Our systematic realist review demonstrates that service users with physical and/or mental health conditions were referred to or prescribed with blue space activities by health, social care, and health-trained professionals.We ofer a synthesised logic model demonstrating how service user-and programmerelated CFs and PTs are associated with and explain the mechanisms of BPP implementation to help improve physical, cognitive (mental), social health, and proenvironmental knowledge of service users.If the implementation of accessible and service user-centred BPPs is sustainably supported by multistakeholder partnerships; funding support; policies; effective communication protocols; skilled health, social care workers; and service providers, then service users are more likely to enrol in, engage with, and adhere to BPPs and experience improvements on their health and wellbeing.With the inaccessibility, long waiting lists, adverse efects, incompatibility, cost, and environmental impacts of conventional healthcare, employing a well-designed BPP implementation model in a suite of healthcare services especially for people with mental health conditions has some benefts.

Data Availability
Te data supporting this systematic review are from previously reported studies, which have been cited.Beginning three months after publication until September 2024, the processed data are available from the corresponding author upon request.

Additional Points
Te following are known about this topic: (i) Blue spaces ofer health benefts alternative to green spaces.(ii) Blue prescription programme (BPP) is an example of naturebased social prescribing characterised by connecting people with blue spaces.(iii) Tere is limited understanding on the contextual factors and programme theories that describe BPP implementation.Tis paper adds the following: (i) Tere are 20 service user-and programme-related contextual factors associated with BPP implementation.(ii) BPP implementation could be explained by programme theories on communication protocols and long-term programme sustainability, in addition to existing programme theories on enrolment, engagement, and adherence of service users.(iii) A holistic logic model (theory of change) demonstrating mechanisms of BPP implementation that could be used in designing, implementing, and evaluating nature-based social prescribing programmes.
Health & Social Care in the Community

8
applicable; a, qualitative component of a mixed-method study; b, quantitative component of a mixed-method study.
Occurrence of contextual factors (CFs) associated with BPP implementation in each studyPatient-

Figure 2 :
Figure 2: Synthesised logic model of blue prescription programme in health, social care, and specialised educational facilities based on included studies.

Table 1 :
Keywords, search strings, and yielded records from database searches.

Table 3 :
Characteristics of blue prescription programmes.

Table 4 :
Co-existence of contextual factors and initial programme theories in investigated studies.

Table 5 :
Final programme theories of BPP implementation.
Counselling about the service users health status and benefits of the intervention Programme Theory 2: Service User Engagement 1. Ensuring compatibility of intervention based on service user preference, skills, and goals 2. Consulting service users about the design of needed adaptive and supportive infrastructure 3. Service users enrol to the programme and attend the initial session