As the complexity of climate, land, water, human health and well-being challenges expand, so too does the need for a focus on the mesoscale for integrative research and scholarship. Attending to the mesoscale highlights the importance of regions and areas that connect and reflect both local and global dynamics, including the social landwaterscapes where place-based actions, affections and affiliations interact with planetary agendas and trajectories.

Watersheds, or catchments, exemplify the mesoscale. There are long-standing and ongoing reasons to consider their boundaries as optimal geographic and political units [1,2] in which regenerative interventions can be applied to achieve ecosystem and health co-benefits [3,4]. Watersheds also often align with Indigenous tenure systems and provide a focusing lens to restore connections between people, places and health. The mesoscale of landwaterscapes also offer integrative contexts for relationships and collaborations that prioritize equity and diversity, and to foster synergies across social, ecological and health outcomes.

Functioning watershed systems provide clean drinking water, flood mitigation, biodiversity conservation and food production, among other key ecosystem services, all making vital contributions to disease prevention, improved well-being and enabling cultural practices. A growing body of evidence from around the world shows how human activities within watersheds are linked with water-related diseases, water security, and decreased downstream availability of ecosystem attributes for food, cultural practice, livelihoods, and lifestyles.

Many, perhaps most, articles in PLOS Water are relevant to the mesoscale but relatively few foreground ‘health in’ or ‘health of’ the watershed per se, and thereby overlook the combined social, ecological and health implications of watershed governance. To rectify this shortfall we have brought together a collection of papers focused on “Watersheds and Health” to profile contemporary efforts focused on integrative watershed approaches as they relate to health of humans, other species, and ecosystems.

Contributors to the collection of papers have taken a variety of approaches to address the scope of “watersheds and health”. Several of the papers have documented case studies, where a river’s catchment, or cluster of catchments, watersheds, or river basins are the location for careful treatment of the interactions between people and their environments, and the consequences for human health, social equity and environmental quality.

RiverOfLife et al. have foregrounded Living Water and Country in a catchment with agency in the Kimberley region of northern Australia [5]; they show how an Indigenous worldview and legal framework of First Law, also known as ‘chthonic law’ sensu [6] can provide the basis for long lasting non-extractive relationships. Awatere et al. show that there has been a resurgence of the use and understanding of Māori knowledge alongside western science in Aotearoa-New Zealand to inform co-governance of catchments [7]. They provide three examples of river catchments where Māori are taking decisive action, and playing a leading role in the co-governance of waterways. Their examples emphasize the ways that health for Māori as Indigenous peoples is fundamentally connected with the health of catchments and ecosystems. Ford and Waters also emphasize this theme, noting that all beings, including land and humans, are in relationship with water; and draw attention to the far-reaching implications of embracing Indigenous co-governance models to protect water and all relations in the watershed [8].

Mendez et al. working in the Colombian Andes sought to enhance the comprehension of watersheds as socioecological entities [9]. Seen through this lens, the authors expose the water-related environmental burdens of communicable and noncommunicable diseases, with health disparities driven by ethnic, gender and socioeconomic status. Resolving such disparities in damaged watersheds requires a place-based, participatory and transdisciplinary approach, as Hadfield et al. demonstrate [10]. Using a Living Lab methodology in the Citarum basin in West Java, Indonesia, Hadfield et al. negotiate complex multi-level governance settings, challenging funding processes, and local social and environmental conditions in response to river pollution and economic imperatives.

Our collection includes two other case studies each drawing on substantial programs of research. Parkes et al. likened integrated watershed research in the Nechako catchment, western Canada, to a braided river, connecting across themes of climate change, water security, sediment sources and dynamics, and watershed governance [11]. Alongside complementary thematic insights they underscored that integrative watershed understanding requires engagement with diverse knowledges and perspectives, fostered by patience, flexibility and the willingness to listen, learn and collaborate with others. Jupiter et al.’s “Watershed Interventions for Systems Health” in Fiji, South Pacific, focused on environmental drivers of ill-health at the scales at which ecological processes occur within water basins [12]. The interventions examined ranged from national and provincial governance, to coordinated actions that simultaneously address critical risks from poor sanitation infrastructure, water supply systems, land use practices, waste management, animal management, drainage, and basic hygiene.

A global review of river health provides an important counterpoint to the emphases found in the other papers in the collection. Using an exclusively biophysical definition of ‘ecosystem health’, Kuenhe et al. identified a common framework of indicators that can be implemented in coordinated global policy, research, and data infrastructure developments, and can also support efforts (even local ones) to monitor river health with protocols that are flexible but sufficiently standardized [13]. The absence of human health, and social indicators, from such a framework reflects the very real sectoral boundaries that challenge efforts toward a meaningful, integrative watersheds and health agenda. The Opinion piece by Hallström underscores this exact challenge; first by using water and watersheds as the integrative lens, and then calling for an innovative form of thinking—an integrative, rather than bureaucratic, scientific, or political rationality [14].

In combination, this collection has highlighted a diverse range of opportunities, challenges and new insights from adopting integrative approaches that overtly address watersheds and health, together. By foregrounding the mesoscale, these efforts and their collective contributions recognize: (a) Indigenous informed approaches to spiritual, physical, and legal boundaries in the landscape; (b) the social and ecological foundations of health; (c) climate resilient, nature-based solutions, including regenerative food and water systems that replace extractive practices with ones built on biodiversity, soil, and water as priority assets; and (d) combined social, ecological and health outcomes arising from integrative governance in watersheds. In keeping with the ecological emphasis, the collection also provides a sense of emergence: where the perspectives gained from across all papers deepens the sense of co-benefits available from future generations of research, education and practice focused on "watersheds and health."