Swimmable
A public map of UK bathing waters and live storm overflow data. This is a work in progress; coverage and methodology continue to evolve.
Data sources
Regulators
- Environment Agency — bathing water classifications, samples, and pollution risk forecasts (England). Open Government Licence v3.0.
- Natural Resources Wales — bathing water classifications and samples (Wales), via the Defra Linked Data Platform. Open Government Licence v3.0.
- Scottish Environment Protection Agency — bathing water classifications and samples (Scotland), via sepa.org.uk.
Water and sewerage companies — Event Duration Monitoring (EDM)
- Thames Water Utilities Limited — first-party Open Data API, under its own Open Data licence; and, in parallel during a verification phase, the thames-sewage mirror, under CC BY 4.0.
- Anglian Water Services, Northumbrian Water, Severn Trent Water, South West Water, United Utilities, Wessex Water, Yorkshire Water — each publishes its Storm Overflow Activity dataset under CC BY 4.0, declared in the operator’s own dataset metadata on ArcGIS Online.
- Wessex Water and Yorkshire Water additionally publish event-level Event Duration Monitoring history feeds, also under CC BY 4.0.
- Scottish Water — current and previous event per overflow, via api.scottishwater.co.uk. Published under Scottish Water’s open licence; users must cite Scottish Water as the data source.
- Welsh Water (Dŵr Cymru) — latest-event snapshot with operator-published bathing-water linkages, via ArcGIS Online. Published under Welsh Water’s open-data programme; specific licence terms for this dataset are pending operator confirmation.
- Southern Water — five-year event history with Genuine / Not-Genuine review flags, via the Rivers & Seas Watch ArcGIS service. Southern publishes its Annual Performance Report under CC BY 4.0 and is publishing additional datasets under an open data licence; specific licence terms for the Rivers & Seas Watch service are pending operator confirmation.
Annual EDM returns (enrichment)
- The Rivers Trust — Event Duration Monitoring Storm Overflow Annual Returns 2024 (England and Wales), via ArcGIS Online, under the Open Government Licence v3.0. Produced by The Rivers Trust. © Environment Agency copyright and/or database right 2024. © Dŵr Cymru/Welsh Water. © Hafren Dyfrydwy.
Ambient water-body baseline (context only)
- Environment Agency — Water Framework Directive water-body boundaries and ecological-status classifications (England), via the Catchment Data Explorer, under the Open Government Licence v3.0. Shown as context on spot pages; never a status input.
Catchment-aware downstream signal
- Alex Lipp, Jonny Dawe and Sudhir Balaji — sewage-map, the project behind sewagemap.co.uk. Per-operator GeoJSON of river reaches downstream of currently-active or last-48-hour CSO discharges, refreshed every ~15-20 minutes. Used with the authors’ permission and republished under CC BY-SA 4.0.
Changes from source data. Every CC BY 4.0 licence requires disclosure of changes made. This map transforms operator data uniformly: Start and Stop alerts (where published) are paired into events; unmatched Starts are assigned a derived 48-hour inferred closure; duplicate rows for the same outfall are collapsed by external ID with last-wins semantics. Computed status verdicts on the map are the project’s, not the operators’.
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Statuses are computed every fifteen minutes from the latest ingested data. Absence of negative signal is not the same as positive confirmation of safety.