About this site

What it is

Can I Swim? answers one question for every bathing water on the regulators’ lists in Britain and Ireland: what is the water quality like today? It reads the official pollution forecasts, the water companies' live storm overflow monitors every half hour, and recent rainfall every three hours, and works out a single answer for each place, with its reasons and its gaps shown.

The named waterfalls in between get a narrower answer, and the difference matters. Nobody tests the water at a waterfall, so there is no verdict on one and there never will be — only how much rain has fallen near it in the last two days, which is what decides whether it is worth the walk. Rainfall there is read every six hours.

There is no account to make, no advertising and no tracking, and it sets no cookies. The beaches and waterfalls you save, and whether you like the map open or closed, are kept in your own browser and never sent anywhere. Two things come from somewhere other than this domain. The map tiles, and only once a map opens — which is when you scroll one into view or press Search. And the photograph on a waterfall page, where there is one: 424 of the 645 named waterfalls have a picture from Wikimedia Commons, and it is loaded from Wikimedia rather than copied here, so scrolling to it tells them your address. That is the licence working as intended — the photographers are credited at the source — but it is a request to somebody else all the same. The map library itself is served from here now, so a map no longer depends on anybody else's uptime. The typeface is served from here rather than from Google, so visiting a page tells Google nothing.

If you turn on warnings for the places you have saved, the list of those places and an address your browser gives us for sending the message do leave your device, because there is no other way to send you one. Nothing else does, and turning it off deletes them.

Who made it, and why

It was built by Jay Horwood, in Hertfordshire, after looking for a straight answer about a beach and finding either an app, a login, or a map that would not say what it did not know. It is not a company and nobody is paid for it. The running cost is a domain name.

The design rule throughout is that the site would rather say “can’t say” than guess. A reading that could not be taken is shown as a reading that could not be taken — never as an all-clear.

Where every number comes from

• England — Environment Agency: daily pollution risk forecasts, open pollution incidents and bathing water classifications.
• Wales — Natural Resources Wales, through the same service.
• Scotland — SEPA: daily predictions for the beaches that get them, and annual classifications for the rest.
• Northern Ireland — DAERA sample results and bathing advice. The annual classifications are the one figure on this site not taken from a feed: DAERA publishes them in a written announcement, as coloured badges inside per-site PDF profiles, and on a dashboard, but not in any machine-readable form. All 33 are copied from DAERA's 2025 announcement and the build refuses to use them unless the spread still matches the totals DAERA published with it.
• Ireland — the EPA and local authorities: statutory bathing restrictions and sample results.
• Storm overflows — the eleven water companies that publish live monitor status, about 18,600 outfalls in all. The number moves as companies add and retire monitors, so it is rounded to the nearest hundred.
• Rainfall — Open-Meteo, modelled rather than measured, and labelled as such wherever it is used.
• Waterfalls — OpenStreetMap contributors, under the Open Database Licence.
• Photographs — Wikimedia Commons, each credited to its photographer on the page it appears.

Every reading carries the source it came from. Anything that decides a verdict — a warning, a discharge, a sample, a rainfall total — carries the time it was taken as well. The weather panel is the exception and says so in its own words: sea temperature, sea state, wind and UV are a forecast for the day rather than a reading at a moment, so they are dated to the day and not to the hour. If a source is unreachable, the page says so rather than falling back on something older and pretending it is current.

What it cannot tell you

• It is not a substitute for the sign at the beach. A warning posted on site by the regulator or the council is the one that counts.
• Neither part of Ireland has live storm overflow data. In the Republic none is published at all. Northern Ireland does monitor: NI Water had 466 event duration monitors by May 2026, covering 31 of its 33 designated bathing waters, but it publishes a summary once a year rather than live status, so it cannot answer whether an overflow is discharging right now. Affected pages say so rather than showing a clear result.
• A monitor can be offline. A silent monitor is not a quiet one, and is counted as unknown, not as clean.
• Waterfalls are not tested by anyone. Their pages answer whether there is water coming over, never whether it is safe to swim.
• Nothing here is a laboratory result for today. Water is sampled every few weeks, not hourly; forecasts are models.

Something wrong?

Corrections are welcome and wanted — a beach in the wrong district, a waterfall under the wrong name, a verdict that does not match the sign in front of you. Please say which place and what you saw.

Reports go into a queue and are read by a person before anything appears on the site. Nothing you send is published automatically.

For journalists

Everything here is derived from published open data and can be checked against the sources above. The code that collects it is public, so any figure on the site can be traced from the page back to the regulator that issued it. Happy to help with specific questions, figures for a given stretch of coast, or historical context.

The code

The collector is open source at github.com/Jay-1983/swim-collector. It runs every half hour and publishes one small snapshot. There is no database of readers. The one thing it does hold is the list of saved beaches for anyone who has turned warnings on, with the address their browser gave for sending the message, because a warning cannot be sent without them — and turning warnings off deletes both.