Ofwat has not fined Thames Water for illegal discharges of untreated sewage into rivers. Regulation of discharges of untreated sewage to the water environment is the responsibility of the Environment Agency (EA) and not Ofwat.
In March 2017, Thames Water was ordered to pay fines of almost £20 million following a series of significant pollution incidents on the River Thames and its tributaries in 2012 to 2014. The fine, for six separate cases, was a record as the highest ever set by the courts in a prosecution brought by the EA. More recently, in July 2019, Thames Water was ordered to pay costs and fines of about £700,000 for pollution from Maidenhead Sewage Treatment Works.