Terms of use

Plain-English terms for using SwimSignal. Last updated 29 September 2026.

Who runs SwimSignal

SwimSignal is a free, non-commercial project run by one person, the owner of the GitHub account ethanbuckley. It is not a company. Email ethan@ethanbuckley.me.uk; the privacy notice says what happens to what you send.

In these terms, "we" and "us" mean the person who runs SwimSignal, and "you" means anyone who uses it. These terms apply whenever you use the site. If you do not agree with them, please do not use it.

SwimSignal is independent. It is not run by, connected with or endorsed by the Environment Agency, any water company, Water UK, Stream, the Met Office, Ordnance Survey, Open-Meteo or OpenStreetMap.

What SwimSignal is

SwimSignal is an experimental tool. It estimates the chance that sewage from storm overflows upstream affects a spot on a river or lake in England, now and over the next few days. On rivers it also estimates the chance that a water sample would fail the E. coli limit for bathing water. It combines the water companies' published overflow data, rainfall forecasts, the river network and statistical models. At designated bathing waters it repeats the Environment Agency's yearly rating and its sampler's latest algae check. It is a forecast, not a measurement.

What it is not

SwimSignal does not test water, and it cannot tell you whether it is safe to swim. Its spill forecast covers monitored storm overflows only. Its E. coli estimate allows for rain washing in pollution from other sources on average, but knows nothing about a particular farm, road, boat, outfall or incident. The algae check is the Environment Agency's observation on the date shown, and it does not tell harmful algae from harmless kinds. The site does not show advice against bathing given at short notice, after pollution or an algal bloom. A "low" reading means nothing the site looks at flags the day. It does not mean the water is clean or safe, and it says nothing about currents, cold water or other dangers. A "high" reading is a probability, not a confirmed spill.

Before you swim

Nothing on this site is advice about your health or safety. Whether to go in the water is your decision.
Do not rely on SwimSignal alone. Check the signs at the water and follow them, and any instructions from lifeguards or the landowner. At a designated bathing water, check the Environment Agency's page for it too: it shows advice against bathing that SwimSignal does not. Each bathing water's page on SwimSignal links to it.
Open water has dangers the site does not cover, among them cold water, currents, weirs, depth, hidden objects and algae.
If someone is in trouble in the water, call 999. If you are unwell after swimming, contact your GP or NHS 111 and say that you have been swimming.

Accuracy

We take care over the site, but we do not promise that anything on it is accurate, complete or up to date. Subject to "Our responsibility to you" below, it is given without responsibility for its accuracy. How often the forecast is right is published on the accuracy page, including where it is wrong. Overflow status can be late, missing or wrong at source; some overflows have no live monitor; rainfall forecasts have errors that grow with lead time; the river network and outfall positions are approximate. Expect the forecast to be wrong some of the time.

Water companies' data

Each overflow's status is shown as its water company publishes it. Whether an overflow is "expected to spill" is our model's estimate, not a statement by the company, and it does not mean the company has broken any rule.

Our responsibility to you

The site is free and provided as it is. Its forecasts can be wrong, late or missing, and so can alerts: if you turn them on, an alert can be late or not come at all, so no alert does not mean the water is clean. We do not promise that the site will be available, secure or free of errors.

Nothing in these terms excludes or limits our liability for death or personal injury caused by our negligence, for fraud or fraudulent misrepresentation, or for anything else that the law does not allow us to exclude or limit.

Subject to that, we are not liable for any loss or damage that comes from using the site or relying on it, including a decision to swim or not to swim, a wasted journey or a cancelled event. If you use the site for a business or to run an event, you do so at your own risk, and we are not liable to you for any loss of profit, income, business or opportunity.

Using the site, its data and its code

You may use and share the site for any lawful purpose. Please do not overload it.
The third-party data in the site's pages and data files (data/spots.json, data/overflows.geojson, data/verification.json, data/alerts.json) and in the project's releases keeps its own licence, listed below. Nothing in these terms limits what that licence lets you do with it.
Our own forecasts, levels and scores may be reused for non-commercial purposes if you credit SwimSignal and keep the data credits below. Ask first about any other use.
The source code is open under the MIT licence. That licence covers the code, not the data.
Links to other websites are there for convenience. We are not responsible for what those sites say or do.

Data sources and credits

Storm overflow status. Storm Overflow Activity data from Anglian Water Services, Northumbrian Water, Severn Trent Water, South West Water, Southern Water (© 2026 Southern Water), Thames Water, United Utilities, Wessex Water (© 2024 Wessex Water) and Yorkshire Water, via the National Storm Overflow Hub. Each is licensed under CC BY 4.0. SwimSignal combines the nine feeds, renames their fields, fills gaps from the Environment Agency's annual returns and models the result.
Spill model training. United Utilities storm overflow event data, 2023 to 2025, via Stream, CC BY 4.0. Used to train and test the spill model; the site publishes only the scores.
Environment Agency data, all under the Open Government Licence v3.0:
- Storm overflow (event duration monitoring) annual returns: © Environment Agency copyright and/or database right 2025. All rights reserved.
- Bathing water ratings and in-season samples: © Environment Agency copyright and/or database right 2016. All rights reserved.
- E. coli results and algae checks from the Water Quality Explorer: © Environment Agency copyright and/or database right 2025. All rights reserved.
- Water Framework Directive lake water bodies: © Environment Agency copyright and/or database right 2015. All rights reserved. Contains Ordnance Survey data © Crown copyright 2013.
River levels, in the server version only: this uses Environment Agency flood and river level data from the real-time data API (Beta), Open Government Licence v3.0. The website does not use them.
Rainfall. Weather data by Open-Meteo.com, CC BY 4.0. For England, Open-Meteo serves the Met Office's UK forecasts: Met Office data © Crown copyright, CC BY-SA 4.0. SwimSignal adds the rainfall up over 24 and 48 hours and uses it in its models; the rainfall figures on the site stay under CC BY-SA 4.0. The models were trained on ERA5-Land reanalysis rainfall from the Copernicus Climate Change Service, and on Open-Meteo's archived forecasts, both via Open-Meteo.
Map. Map data © OpenStreetMap contributors, under the Open Database Licence; map tiles from the OpenStreetMap Foundation. The map library is Leaflet (BSD 2-Clause licence).

The data files listed above carry a shorter version of these credits in a credits field. None of these bodies endorses SwimSignal.

Changes to these terms

These terms may change as the tool develops. The date at the top is the date of the current version. Earlier versions are kept in the file's history.

Law

These terms are governed by the law of England and Wales, and the courts of England and Wales can hear any dispute about them. If you live in Scotland or Northern Ireland, you can also bring proceedings in your local courts. If a court decides that part of these terms cannot be enforced, the rest still applies.