A huge mass of used wet wipes has formed an 'island' that has changed the course of (the Thames)

[muriel_volestrangler]

10. Not all the time, but they do in heavy rainfall, or when blockages happen

Exclusive: water firms discharged raw sewage into England's rivers 200,000 times in 2019

The figures, obtained via environmental information requests, trace releases of sewage from storm drains in rivers across England by all nine water companies and provide a comprehensive picture of the scale of pollution from what critics say is the routine dumping of untreated sewage.
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Countries are legally obliged to treat sewage before it is released into waterways. Discharges of untreated human waste are permitted only in “exceptional circumstances” for example after extreme rainfall, the European court of justice has ruled.

But the scale of the sewage releases in 2019 reveals what one industry insider said was the frequent and routine nature of discharging untreated effluent from storm overflows.
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He said the industry had for years ignored warnings about the growing scale of spills from combined sewer overflows (CSOs) – storm pipes that allow rainwater, untreated sewage and runoff to discharge into waterways.

https://www.theguardian.com/environment/2020/jul/01/water-firms-raw-sewage-england-rivers

Combined Sewer Overflows Explained

England has a combined sewage system made up of hundreds of thousands of kilometres of sewers, built by the Victorians, in many urban centres. This means that clean rainwater and waste water from toilets, bathrooms and kitchens are conveyed in the same pipe to a sewage treatment works.

During heavy rainfall the capacity of these pipes can be exceeded, which means possible inundation of sewage works and the potential to back up and flood peoples’ homes, roads and open spaces, unless it is allowed to spill elsewhere. Combined sewer overflows (CSOs) were developed as overflow valves to reduce the risk of sewage backing up during heavy rainfall.

Overflows of diluted sewage during heavy rainfall are not a sign that the system is faulty. Combined sewer overflows (CSOs) are a necessary part of the existing sewerage system, preventing sewage from flooding homes and businesses.
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CSOs can discharge through misuse of the system. Wet wipes make up more than 90 per cent of the material causing sewers to block. We work with partners to raise awareness of this issue and the need to reduce the pressure put on the sewerage system through the #BinIt4Beaches campaigns.

https://environmentagency.blog.gov.uk/2020/07/02/combined-sewer-overflows-explained/