Around 600 million litres of sewage-contaminated water could be entering an Essex river and its tributaries every year through unpermitted and previously unmonitored outfalls.
The volume is equivalent to around 240 Olympic-sized swimming pools of polluted water flowing through the River Roding, according to a new citizen science study.
The waterway begins in rural Essex before flowing through East London and joining the River Thames at Barking Creek. The Lower Roding catchment stretches between Chigwell and Barking.
A six-month study, led by environmental charities Thames21 and the River Roding Trust, monitored more than 70 outfalls across the Lower Roding and its tributaries.
Researchers combined water quality testing with flow measurements to identify the biggest sources of pollution.
Sewer misconnections and faulty drainage infrastructure were identified as major contributors, with sewage discharges continuing during dry weather when there is less rainfall to dilute pollutants.
Chris Coode, CEO of Thames21, said: “Our rivers deserve to be clean and healthy, yet these findings reveal an unacceptable threat to water quality, wildlife and local communities.
“The Environment Agency, Thames Water and Redbridge Council must take swift action to address the critical issues identified through this citizen science monitoring programme.”
Cran Brook, a tributary of the river, was identified as the single biggest source of sewage pollution in the area. Researchers linked the contamination to faulty infrastructure, widespread misconnections and landfill leachate from a historic landfill site.
The charities are calling for the brook to be prioritised for restoration. This includes repairs to sewage infrastructure, the correction of misconnections and measures to prevent landfill leachate entering the river.
Paul Powlesland, Founder of the River Roding Trust, said: “We now need Thames Water and the Environment Agency to fix the most damaging illegal outfalls as a matter of emergency.
“We also need the government to carry out a similar survey on every river in England; otherwise how can we fix a problem we do not know the extent of?”
The organisations also want nature-based solutions, including wetlands, to help reduce pollutants reaching the watercourse.
Thames21 are calling for a national strategy to have mandatory drainage checks for new build homes and when properties are sold.
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