Anglian Water storm overflows in 2025
What the official annual return shows for Anglian Water’s storm overflows in England, compared with 2024 and with the other water companies.
Summary
The 2025 annual return lists 1,442 storm overflows run by Anglian Water in England. 1,438 have a usable spill count. Together they recorded 17,322 spills and 105,806 hours of discharge. The median outlet recorded 6 spills and 13.5 hours.
For a fair comparison with 2024, we use only the 1,253 outlets with a count in both years and a monitor that worked at least 90% of each year. Their spills went from 38,283 to 15,295, a fall of 60%. 956 recorded fewer spills and 166 recorded more.
244 outlets (17%) recorded no spills in 2025. 39 (2.7%) recorded 60 or more.
Anglian Water’s median of 6 spills per outlet is the 9th highest of the 10 companies in the return. The England median is 11.
119 outlets had a monitor that worked for less than 90% of the year. Counts from those outlets may be low.
- 1,442
- Outlets listed
- 17,322
- Spills in 2025
- 6
- Median per outlet
- 105,806
- Recorded hours
How many spills each outlet recorded
Outlets with a usable 2025 count, grouped by the number of spills. The longest bar is the largest group.
- 0
- 244 17%
- 1 to 9
- 652 45.3%
- 10 to 19
- 247 17.2%
- 20 to 39
- 200 13.9%
- 40 to 59
- 56 3.9%
- 60 or more
- 39 2.7%
Spills over time
The median outlet run by Anglian Water recorded 6 spills in 2025, against 11 across England.
1,253 outlets have a comparable count for both 2024 and 2025, with the monitor working at least 90% of each year. 166 recorded more spills, 956 fewer and 131 the same. Together they went from 38,283 to 15,295 spills, a fall of 60%.
Largest rises from 2024 to 2025
- Knossington STW5 → 93
- Normanby-Park Sp3 → 48
- Ipswich-Wherstead Rd Sp7 → 47
| Year | Outlets with a count | Total spills | Median per outlet | England median |
|---|---|---|---|---|
| 2025 | 1,438 | 17,322 | 6 | 11 |
| 2024 | 1,431 | 43,825 | 18 | 19 |
| 2023 | 1,295 | 29,168 | 9 | 20 |
| 2022 | 969 | 15,041 | 8 | 13 |
| 2021 | 757 | 19,756 | 13 | 19 |
Earlier returns list fewer of these outlets, so totals are not comparable between years. The median per outlet and the like-for-like change are fairer comparisons. Counts are events, not volume.
Largest falls from 2024 to 2025
Only outlets with a count in both years and at least 90% monitor operation in each. Counts depend on rainfall as well as on the sewer network, so a fall does not show on its own that an overflow improved.
- Horning-Knackers Wood STW203 → 13
- Feltwell STW192 → 12
- Geddington STW203 → 23
- Teversham STW167 → 0
- Stoke Bruerne STW179 → 19
- Whitton STW170 → 13
- Odell STW165 → 10
- Peterborough (Flag Fen) STW185 → 31
- Southend-Woodgrange Drive CSO 1165 → 13
- Welton STW (Northants)247 → 99
Most spills in 2025
- 1Grimsby-Pyewipe So Wrc155spills
The River Humber
- 1Hallaton STW155spills
Medbourne Brook River Welland
- 3Ramsey STW145spills
The Ramsey High Lode
- 4Thorpe Malsor STW118spills
Shutlanger Brook
- 5Great Easton STW (Leics)111spills
River Welland NT
- 5Manthorpe STW111spills
East Glen River
- 7Nettleham STW109spills
Nettleham Beck
- 8Foxton WRC (Cambs)102spills
River Rhee · monitor 87.4%
- 9Welton STW (Northants)99spills
Whilton Branch River Nene (NT)
- 10Southend STW94spills
Thames Estuary · monitor 28%
Most hours in 2025
- 1Great Easton STW (Leics)1,895hours
River Welland NT
- 2Foxton WRC (Cambs)1,645hours
River Rhee · monitor 87.4%
- 3Nettleham STW1,585hours
Nettleham Beck
- 4Great Oxendon STW1,548hours
River Ise
- 5Ramsey STW1,432hours
The Ramsey High Lode
- 6Pertenhall STW1,273hours
Keysoe Brook. River Kym NT
- 7Whaddon STW1,250hours
Calverton Brook
- 8Welton STW (Northants)1,239hours
Whilton Branch River Nene (NT)
- 9Hollowell STW1,190hours
Brampton Branch R.Nene NT
- 10Hallaton STW1,126hours
Medbourne Brook River Welland
Waterbodies with the most spills
Total 2025 spills from outlets the return links to each waterbody. A waterbody with more outlets will usually have a higher total.
| Waterbody | Outlets | Spills | Spills per outlet |
|---|---|---|---|
| Thames Lower | 49 | 471 | 9.6 |
| Middle Level | 24 | 357 | 14.9 |
| Ancholme from Bishopbridge to the Humber | 15 | 282 | 18.8 |
| Witham - conf Cringle Bk to conf Brant | 13 | 278 | 21.4 |
| Humber Lower | 5 | 275 | 55 |
| Welland - conf Langton Bk to conf Gwash | 15 | 273 | 18.2 |
| Norfolk East | 11 | 268 | 24.4 |
| Bure & Waveney & Yare & Lothing | 15 | 254 | 16.9 |
| Ise - Upper | 14 | 247 | 17.6 |
| Waveney (Ellingham Mill - Burgh St. Peter) | 15 | 247 | 16.5 |
How to read this report
- A spill is a counted event under the 12/24-hour method. It is not a volume, and it does not measure harm or water quality.
- Missing counts are left out, not treated as zero. Low monitor operation can make a count too low.
- Rankings compare counts only. They do not show whether an overflow broke its permit or the law.
- Earlier years list fewer outlets, so compare medians or like-for-like groups, not totals.
Data: Environment Agency event duration monitoring annual returns, Open Government Licence v3.0. How spills are counted · How the data works · Sources