Storm overflows in England: 2025 report

What the official 2025 annual return shows across England’s storm overflows, how it compares with 2024, and how the water companies differ.

Summary

The 2025 annual return lists 14,303 storm overflows in England. 14,239 have a usable spill count. Together they recorded 292,119 spills and 1,878,240 hours of discharge. The median outlet recorded 11 spills and 22.3 hours.

For a fair comparison with 2024, we use only the 12,221 outlets with a count in both years and a monitor that worked at least 90% of each year. Their spills went from 403,424 to 258,514, a fall of 36%. 8,501 recorded fewer spills and 2,223 recorded more.

2,231 outlets (15.7%) recorded no spills in 2025. 1,144 (8%) recorded 60 or more.

1,039 outlets had a monitor that worked for less than 90% of the year, and 35 gave no operation figure. Counts from those outlets may be low.

14,303
Outlets listed: 292,119
Spills in 2025: 11
Median per outlet: 1,878,240
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: 2,231 15.7%
1 to 9: 4,517 31.7%
10 to 19: 2,275 16%
20 to 39: 2,723 19.1%
40 to 59: 1,349 9.5%
60 or more: 1,144 8%

Spills over time

12,221 outlets have a comparable count for both 2024 and 2025, with the monitor working at least 90% of each year. 2,223 recorded more spills, 8,501 fewer and 1,497 the same. Together they went from 403,424 to 258,514 spills, a fall of 36%.

Largest rises from 2024 to 2025

Prees - Mill Street (CSO)0 → 151
Crosby Garret WwTW24 → 159
Laburnham Grove4 → 102

Year	Outlets with a count	Total spills	Median per outlet
2025	14,239	292,119	11
2024	14,150	449,788	19
2023	8,166	283,021	20
2022	6,943	159,876	13
2021	5,228	169,273	19
2020	2,520	84,906	18

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.

Lower Moor STW (CSO)Severn Trent Water225 → 18
Cartmel In Cark Pumping Station (Site ID CARTC) (LAK0099)United Utilities236 → 30
Amersham balancing tanks/amersham vale stkThames Water210 → 13
Horning-Knackers Wood STWAnglian Water203 → 13
Roborough STW SSO RoboroughSouth West Water327 → 143
Langthorne/No 2 STWYorkshire Water282 → 101
Feltwell STWAnglian Water192 → 12
Geddington STWAnglian Water203 → 23
KIRK BAMPTON WwTWUnited Utilities204 → 29
Swinton Masham/No 2 STWYorkshire Water229 → 62

Most spills in 2025

1
Croyde STW So Croyde
South West Water
253spills
2
Melton/STW
Yorkshire Water
245spills
3
Shop STW So Shop
South West Water
243spills
4
Salcombe Regis STW So Salcombe Regis
South West Water
235spills
5
Horns Cross STW So Horns Cross
South West Water
230spills
6
Lock Lane CSO
United Utilities
217spills
7
Town Quay Spst Pscsoeo Fowey
South West Water
198spills
8
Abbotsham STW So Abbotsham
South West Water
196spills
9
Tatworth STW SSO Tatworth
South West Water
189spills
10
Lydney STW (SSTO)
Severn Trent Water · monitor 89.7%
178spills

Most hours in 2025

1
Salcombe Regis STW So Salcombe Regis
South West Water
5,446hours
2
Shop STW So Shop
South West Water
4,967hours
3
Tatworth STW SSO Tatworth
South West Water
4,141hours
4
Brayford STW So Brayford
South West Water
3,763hours
5
Lavant No.1 SSO - 115745
Southern Water
3,583hours
6
Chacewater STW SSO Chacewater
South West Water
3,542hours
7
Markyate STW
Thames Water
3,531hours
8
STAVELEY WwTW
United Utilities
3,395hours
9
Altarnun STW SSO Altarnun
South West Water
3,295hours
10
Church Stretton STW (SSTO)
Severn Trent Water
3,257hours

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
Tyne	177	3,605	20.4
MERSEY - Transitional	78	2,312	29.6
Bristol Avon (By Bk to Netham Weir)	126	2,053	16.3
Aire from Gill Beck (Baildon) to Wyke Beck	85	2,032	23.9
Mersey (upstream of Manchester Ship Canal)	51	1,711	33.5
Tame (Swineshaw Brook to Mersey)	47	1,480	31.5
Ouse from River Nidd to Stillingfleet Beck	41	1,405	34.3
Irwell (Croal to Irk)	56	1,216	21.7
Bristol Avon	70	1,193	17
Calder from Ryburn Confluence to River Colne	39	1,128	28.9

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

Water companies compared

Companies run different numbers of overflows, so compare the median and the share of outlets with 60 or more spills rather than totals. The change uses only outlets counted in both years with at least 90% monitor operation.

Company	Outlets	Spills	Median	60 or more	Change since 2024	Monitor under 90%
Anglian Water	1,442	17,322	6	2.7%	−60%	119
Dŵr Cymru Welsh Water	122	2,843	14.5	8.2%	−47%	5
Northumbrian Water	1,561	27,860	11	4.6%	−33%	202
Severn Trent Water	2,452	36,471	8	3.1%	−41%	90
South West Water	1,365	46,164	21	20.8%	−19%	45
Southern Water	977	15,554	7	4.6%	−48%	115
Thames Water	581	9,189	6	5%	−61%	32
United Utilities	2,270	60,843	15	14.1%	−23%	194
Wessex Water	1,346	24,442	11	4.8%	−45%	34
Yorkshire Water	2,187	51,431	16	9.5%	−26%	203

Dŵr Cymru Welsh Water figures cover only its outlets in England.