SwimSignal

For event organisers

For triathlons, open water swims and club sessions at a listed spot: the forecast for the day, the storm overflows upstream of the venue, a checklist and a sign to print.

British Triathlon's water quality guidance says that testing a river before an event is likely to be of limited value, and that organisers should understand the overflows upstream and be told when they discharge. SwimSignal forecasts each listed spot from those overflows and the rain, for the day it is issued and the four after it.

Listed spots only, not a point clicked on the map.

Before the event: a checklist

Drawn from British Triathlon's water quality guidance (2025) and Swim England's outdoor swimming guidance for clubs (June 2025). Read both: they cover much more than water quality.

  1. Know what drains into the water. Early in planning, find the streams, drains and sewage outlets that feed the venue, and the farmland, livestock and birds near it. A spot picked above lists the monitored storm overflows upstream; the landowner, the council or the Environment Agency may know of other outlets.
  2. Be told when the overflows discharge. Ask the water company how to be notified when the overflows that matter to your venue spill, and watch its live map in the days before.
  3. At a bathing water, read the Environment Agency's page. From May to September the Agency samples designated bathing waters and publishes the results and any warnings there.
  4. Plan any testing with a laboratory. A sample shows the water when it was taken, and the result takes at least 48 hours. On a river, testing before the event tells you little, because the water changes with flow and rain; ask a UKAS-accredited laboratory what is worth doing. For a one-off event British Triathlon suggests tests a month, two weeks and a week before, the last in time to change plans.
  5. Take a sample on the day. The result comes after the event, but it shows the conditions if swimmers fall ill.
  6. Watch the rain. Heavy rain washes in runoff, makes overflows spill and changes the flow and the water level at the way in and out. The forecast on this page covers the event day from four days before.
  7. Decide the fallback early. Agree who decides, by when, and what happens instead, such as a shorter or moved course or no swim, and tell swimmers how they will hear.
  8. Look for algae. Check by eye every week from a month before, along sheltered shores especially.
  9. Tell swimmers the simple precautions. Cover cuts, do not swim when unwell, wash hands before eating, and shower and rinse kit afterwards.
  10. After the event. Anyone who is ill in the three weeks after should contact their GP or NHS 111 and say that they swam in open water, and where.

The terms of use say what reuse they allow, and what SwimSignal takes responsibility for when it is used to run an event.