Story · Environment map · about 5 min
England's storm overflows: how often they spill, and what that means for the beaches
When heavy rain overwhelms the sewers, storm overflows let a mix of rainwater and sewage into rivers and the sea. Every overflow now has a monitor, and the water companies report each year how often it opened. This story steps through what those returns show, then asks whether the beaches each overflow can affect actually test worse.
Thousands of overflows
Water companies report 14,303 storm overflows in England. In 2025 their monitors counted 292,119 spills lasting 1.88 million hours in total. Each dot is one overflow: blue is none recorded, then yellow through dark red for 1 to more than 100 spills. 1,039 overflows (7%) had a monitor working for less than 90% of 2025, so their true count may be higher. A spill count says how often an overflow opened and nothing about what came out. Click any dot to draw its own five-year history.
Five years, very different totals
The counted spills were 372,525 in 2021, 301,091 in 2022, 464,056 in 2023, 450,398 in 2024 and 292,119 in 2025. The most were in 2023 and the fewest in 2025. Spills follow rain, so a fall is not automatically an improvement. Earlier years on the map show fewer dots than the national totals, because only overflows that can be matched to today's are drawn.
It depends where you live
South West Water averaged 34.0 counted spills per overflow in 2025, against 12.0 for Anglian Water. Across England 49% of overflows spilled 10 times or fewer. Look at the density of red in Devon and Cornwall.
Most bathing waters have a linked overflow
311 of England's 464 designated bathing waters are named by at least one storm overflow's 2025 return. The rest have none recorded in this data, so they are left out of the comparison rather than assumed to have zero spills.
Worse-rated waters see more spills, on average
Waters rated Excellent or Good average 85.3 spills a year at their linked overflows; waters rated Poor or Sufficient average 199.7, noticeably more. Across all 311 linked sites, quality and spill count correlate at 0.22: a real link, in the expected direction, but a weak one.
Why it is not a clean story
Wallasey, rated Good, is linked to 1,611 spills in 2025, the most of any bathing water in this data. Plymouth Hoe East, rated Excellent, still saw 1,417. Water quality is graded from bacteria samples taken through the bathing season, so tides, dilution and the timing of a sample can all keep a heavily-spilled beach testing clean.
Scotland and Wales: not tested here
This comparison is England only: the water companies' overflow returns used here cover England, and the test needs both a bathing-water class and a spill count for the same place. The map shows Scotland's own classification, made by SEPA (the Scottish Environment Protection Agency): the same four grades as England's, Excellent, Good, Sufficient and Poor, but worked out separately, with SEPA's own bathing season (1 June to 15 September), so a Scottish grade is not directly comparable with an English one. Scottish Water's live overflow status is measured differently again, so this map shows the two side by side without claiming the same result holds there.
For classrooms and curious minds
Questions to talk about, alone or in a group.
- Why are storm overflows needed at all, and what makes them spill more in some years?
- Why might a beach with many nearby spills still be rated Excellent?
Try it on the map: Choose a beach you know. How many linked overflows does it have, what is its rating, and how many times did they spill in the latest year?
The figures above are calculated from the datasets listed on Data & sources and are approximate: many map layers are modelled or interpolated. Read each layer’s caveats on the map.