Can outdoor swimming help treat depression – and reduce pressure on talking therapies?

Depression affects at least one in ten people during their lifetime, and the costs – human and financial – are enormous. Standard treatments work for many, but recovery rates remain modest. Waiting lists for talking therapies are long. Antidepressants don't suit everyone. Meanwhile, a growing body of anecdotal and observational evidence suggests that outdoor swimming might help – but robust evidence to support its use in treating depression was limited.

The OUTSIDE1 study set out to answer a practical question: could a randomised controlled trial of outdoor swimming for depression actually work? And if so, what might the early results tell us?

Our approach and partners

Led by the University of Portsmouth and Sussex Partnership NHS Foundation Trust, the trial recruited 87 adults with mild to moderate depression through social prescribing pathways, social media, and word of mouth. Participants were randomly allocated to either an eight-session outdoor swimming course alongside their usual care, or usual care alone.

The swimming sessions – held in the sea, lakes, and outdoor pools – were run by qualified coaches trained in mental health awareness. The emphasis was on water safety, confidence, and enjoyment rather than competitive performance. Participants in the control group continued with their existing treatment, which could include medication, therapy, or other social prescribing activities.

Oxford Population Health's Health Economics Research Centre, supported through ARC OxTV, led the health economic evaluation – helping establish whether a full-scale trial could determine if outdoor swimming offers good value for money as well as clinical benefit.

What we found – and why it matters

1. A full-scale trial is feasible. Nearly all criteria for progressing to a definitive randomised controlled trial were met. Intervention completion reached 79% – fractionally below the 80% threshold, but close enough to proceed with design adjustments.
2. Depression-specific therapy use fell in the swimming group. A lower proportion of participants in the swimming arm reported using depression-specific therapy at both post-treatment and follow-up, compared with the usual care group. Use of antidepressants and sleeping tablets also reduced more in the intervention arm over the study period.
3. Quality of life improved. Participants who swam reported higher average health-related quality of life after the intervention, and this persisted at follow-up. Those receiving usual care alone saw their quality of life deteriorate.
4. Wellbeing benefits extended beyond mood. Outdoor swimming had a moderate positive effect on mindfulness and connectedness to nature. There was a smaller effect on self-compassion shortly after the intervention, though no measurable effect on loneliness.
5. Participants preferred weekly sessions. Focus group feedback indicated that participants found the intervention enjoyable but would have preferred once-weekly rather than twice-weekly sessions – a practical insight for future programme design.

The feasibility study was published in Mental Health and Physical Activity, and a short film co-produced with members of the Lived Experience Advisory Panel captures participants' experiences of outdoor swimming.

What this means

These are early findings from a feasibility study, not definitive evidence. But they point in a consistent direction: outdoor swimming, delivered safely alongside usual care, may improve quality of life and reduce use of depression-specific therapy and medication. If confirmed in a larger trial, this kind of nature-based intervention could broaden the options available through social prescribing – offering something genuinely different to people for whom standard treatments alone are not enough.

What needs to happen next

A full-scale randomised controlled trial – OUTSIDE2 – is now underway, with results expected later in 2026. That trial needs to confirm whether the promising signals from OUTSIDE1 hold at scale, and the health economic evaluation will be critical in determining whether the NHS should commission outdoor swimming programmes as part of social prescribing pathways.

Commissioners and social prescribing leads should watch for those results. If OUTSIDE2 confirms cost-effectiveness, the practical infrastructure – trained coaches, suitable venues, referral pathways – will need to be in place to move quickly from evidence to access.