Research

What SwimSignal is testing and trying before it becomes part of the forecast. Each item says what it is, how far it has got, where its record is, and what would make it part of the forecast pages. None of it changes a spot's level.

Observations you can look at

Satellite lake observations

Dated Sentinel-2 satellite readings of how green the water looked at English lakes, with how many images were clear enough to read and how old the latest is. Laboratory chlorophyll measurements are shown apart where the Environment Agency has them.

Status: observations, shown as they are. The index followed laboratory chlorophyll in a test but missed its stated bar, so it is not turned into a chlorophyll figure, an algae warning or swimming advice. Images are read for May to September at every location. Five pilot locations (Rutland Water, Derwent Water, Frensham Great Pond, Little Sea and Barton Broad) are also checked for new images weekly, and each says when it was last checked; their readings from outside May to September are experimental. Every other location is the historical record: nothing newer than the last season is shown as current.

Measured lake temperatures

Water temperatures the Environment Agency measured in English lakes, May to September from 2000 to 2026, by month: the middle reading and the middle half, with how many readings each figure rests on. Twenty swim spots on those lakes link to their lake.

Status: past measurements at the Environment Agency's sampling points, not today's temperature and not the temperature where you get in.

Spill durations

How long storm overflow spills lasted in 2024 and 2025, from the water companies' start and stop records published by the Environment Agency: each company's typical and long spills, how often a spill already running was still running hours later, and the overflows upstream of each spot. Each spot's overflow history page shows its own.

Status: a record of the past, not a forecast of when a spill will end, and nothing about how much was discharged. Companies record spills differently, so a difference between them may be in the recording.

E. coli samples

Every Environment Agency lab sample of E. coli at the 38 inland bathing waters, from May 2023 to the end of September 2026, each with its date, its count and the lab's limits in words. Beside each, a model estimate worked out afterwards, never shown on the site at the time, and why a sample has none.

Status: a dated historical record. A sample is the water at that place and time only, and the estimate is not the forecast the site issued. Official advice and each bathing water's rating stay on its own page.

Prototypes you can try

Each opens on a spot's own page, added to the address. They are prototypes: the words and the layout may change, and each needs a check with swimmers before it is shown to everyone.

What changed in the inputs

Under a level that moved, the inputs that changed beside it: spills reported, the rain forecast, time passing, or what SwimSignal can see. It lists facts beside the change; it does not say what caused it.

Try it on your saved spots. Status: prototype. Its record. To become a feature: a check that readers can tell a change in the water from a change in what SwimSignal knows.

Evidence map

Where the forecast for a spot has live evidence upstream and where its knowledge ends: overflows with and without a live status, the 60 km limit of the trace, and the samples and gauges near the spot.

Try it at Symonds Yat, where no overflow upstream reports live, or at Ilkley, where most do. Status: prototype. Its record. To become a feature: a check that a sparse map is never read as clean water.

Arrival guide

A spot's practical guide in the order of a first visit: getting there, the path, getting in and out, then who can swim, and what nobody has checked.

Try it at Ilkley. Status: prototype, one spot. Its record. To become a feature: a check on site, and a first-time visitor following it.

Catchment replay

The last 48 hours upstream of a spot: the spills the companies' feeds reported, and when their water was modelled to arrive.

Try it at Ilkley. Status: prototype. Its record.

Tests and their results

Every change to the forecast model is tested against past data first, under rules written down before the scores are seen; many fail, and are kept as records. How accurate the forecast is, how it works, and every test's record in the project's documents.

How a prototype becomes part of the forecast pages

1. It answers one question a swimmer asks, with a way to tell whether it does.
2. It says only what its data holds, with each fact's source and date, and says what it does not know.
3. It works on a phone, offline where the page does, and with a keyboard.
4. Swimmers who have not seen it before can read it without help.
5. The decision to show it to everyone is recorded with the change.