Sewage overflows release a chemical cocktail of sewage, contaminants from roads, household chemicals, and rainwater directly into our rivers and the ocean.

In this section:

How our sewer system works


An outdated system

The UK is riddled with a crumbling network of sewage pipes that leak and overflow beneath our feet. Our combined sewerage network mixes both sewage effluent and surface water runoff to be treated at one of the thousands of wastewater treatment plants dotted around the country. This system can become overwhelmed at times of heavy rainfall. Over 23,000 sewage overflows, installed throughout the network, are designed to take the pressure off the system when it becomes overloaded, preventing overflowing drains and sewage backing up into our homes. However, these overflows release a chemical cocktail of sewage pollution, agricultural pollution, contaminants from roads, household chemicals, and rainwater directly into our rivers and the ocean. They are therefore intended to be for emergency use only, during periods of ‘exceptionally heavy rainfall’.1

What is a sewage over­flow?

Sewage overflows, sometimes referred to as combined sewage overflows (CSO) or pumping stations, are part of our sewerage infrastructure owned and maintained by water companies. They are designed to discharge untreated wastewater in periods of exceptional rainfall to stop sewage backing up into people’s homes.

However, water companies are using sewage overflows more than they should to dispose of sewage causing dangerous levels of pollution in the ocean and inland waterways.

Surfers Against Sewage accesses data on when sewage overflows discharge pollution into 388 of our most popular beaches and river locations. We provide this information to water lovers across the country through our free mobile app, the Safer Seas & Rivers Service (SSRS). As the UK’s only real-time sewage pollution information service, the SSRS helps people to make an informed decision on the risks of going for a surf or taking a dip. Between 1st October 2021 and 30th September 2022, we issued a total of 9,216 sewage pollution alerts for locations included in the SSRS, 2,053 notifications were during the 2022 bathing season alone. Through the app, water users across the country are also taking direct action to end sewage pollution by; writing to local MPs when sewage is pumped onto beaches or rivers, calling out water company CEOs on their polluting habits, and submitting sickness reports on when and where they fell ill after swimming in our wild waterways.

What’s in store?

In this report, we’ve used data collected through the SSRS between 1st October 2021 and 30th September 2022 to focus on the hidden health crisis caused by sewage pollution. We’ve crunched the numbers behind 720 health reports, highlighting the extent to which sewage pollution is literally making us sick. And we’ve delved into some shocking stories from the ocean and river lovers who have fallen ill this year after taking a dip.

Secondly, we’re using data from the Met Office and the SSRS to investigate possible ‘dry spill’ events. These are instances where a sewage overflow has discharged when there has been no rain. Since the law states that sewage should only be discharged in ‘unusually heavy rainfall’, a ‘dry spill’ can indicate illegal activity. We’ve looked at instances when we received notifications of sewage discharges at locations on the SSRS but no rainfall has been recorded in the area. We’re using this information to call out water companies on possible illegal practices.

And finally, for this year’s report we’ve teamed up with Top of the Poops to analyse sewage data from every sewage overflow affecting bathing waters in England from the 2022 bathing season (15th May – 30th September). Together we’ve discovered the number of times and for how many hours untreated sewage water has been dumped into our bathing waters this summer, and by whom.

Next chapter