Across the UK, untreated sewage is discharged into rivers daily.

Water Pattern - Wildfish

How sewage gets into our rivers

Sewage pollution is released into rivers through Combined Sewer Overflows (CSOs).

CSOs are emergency infrastructure systems that are permitted to discharge untreated waste water during periods of heavy rain. They are an important part of our sewage infrastructure and designed to stop sewage backing up into our homes during extreme rainfall events.

Sewage Pollution - Wildfish
Sewage Pollution - Wildfish
Sewage Pollution - Wildfish

Water companies are breaking the law

Water companies routinely use CSOs to release sewage into rivers, even after dry weather. They do this because they have failed to invest in the necessary sewage infrastructure to keep pace with population growth and climate change.

On top of this, regulators are failing to enforce existing legislation. In the rare cases where there are financial penalties, these are easily built into ‘operating costs’ and do not reflect the true environmental damage caused.

Water companies have no incentive to change their environmentally damaging behaviour.

Key Stats

Across the UK, untreated sewage is discharged into rivers daily.



Hours worth of untreated sewage was released into rivers and streams in 2021.


Discharges of untreated sewage into UK rivers in 2021.



Profits water companies have made since privatisation.

The impact of sewage on fresh water


Sewage results in poor water quality

In 2020, 36% of English waterbodies failed their ecological targets because of sewage and wastewater discharged by water companies.


Reduces biodiversity and damages ecosystems

Sewage contains high volumes of nitrogen and phosphorus. In excess, these nutrients can stimulate the growth of algae which starves freshwater species of oxygen. In turn this disrupts natural food chains.

What is needed to protect wild fish and water from untreated sewage?

Urgent investment in sewage infrastructure

Water companies need to invest in sewage infrastructure that is fit for purpose. This should not be at the expense of the customer.

Water companies need to end the routine use of CSOs.

Enforced regulation

Environmental regulators need the resources and funding to enforce current legalisation and hold polluters to account.

Polluters must pay penalties that reflect the true environmental damage being caused.

Independent monitoring

Independent, continuous monitoring of sewage discharge should be mandatory. 

Water companies should not be allowed to monitor themselves as they do currently. This is known as operator self-monitoring.


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