Anglian Water has been fined £1.6m after repeated sewage pollution on the River Brain over six weeks in 2022.
District judge Timothy King heard that Anglian Water’s local mismanagement led to a general decline in water quality between April and June that year.
The company ignored alarms telling them that poorly-treated sewage was being discharged into the river due to the faulty valve. Staff did not talk to each other about the incidents.
The resulting pollution stretched for nearly 14km along the Brain between Braintree and Witham.
The problem was picked up by Environment Agency monitors showing levels of toxic ammonia.
These were the highest recorded in the river over the previous 10 years.
An Environment Agency investigation traced the source to Anglian Water’s water recycling centre in Braintree.
A faulty valve, broken for a week before the first incident in April 2022, led to a semi-solid sludge, usually removed from sewage by water companies, being released into the river.
Further discharges in late May, similar to the first one, led investigators to track the poisonous substance as it snaked along the river.
According to Marcus Sibley, water industry regulatory manager for the Environment Agency in East Anglia, the incidents were a result of "organisational failure."
He said: “We have significantly ramped up our scrutiny of the water industry, and will take enforcement action where we find performance doesn’t meet the standards that communities deserve."
Environment secretary Dame Angela Eagle said: “Anglian Water have clearly been too slow to act in this case and the environment has paid the price.
“The government is overhauling the water system to give the public control.
"Tougher regulation, stronger enforcement and greater accountability, so water companies deliver for customers and the environment.”
The Environment Agency charged Anglian Water with causing a discharge of untreated sewage into the River Brain outside of its environmental permit for Braintree water recycling centre, between 13 April and 2 June 2022.
The company was also charged with failing to comply with the permit, as a separate offence.
Sitting at Cambridge magistrates’ court on October 15, district judge King also ordered Anglian Water to pay costs of £27,334, and a £190 surcharge.
Elsewhere, Anglian Water has admitted polluting the Thames Estuary on two occasions.
The company last week pleaded guilty to discharging sewage and other harmful material off Southend in 2021 and 2022. They will be sentenced next April.
The Environment Agency’s regulation of water companies has increased sharply in recent years, with extra funding from central government to enable more inspections of water treatment plants and other facilities.
In the 12 months to March, officers completed nearly 1,800 inspections of Anglian Water’s wastewater sites, with more than 830 actions identified to improve their operations.
Anglian Water was classified as a two-star-performing company in the last environmental performance assessment carried out by the Environment Agency.
Water companies in England have been successfully prosecuted by the Environment Agency more than 70 times since 2015, securing £169m in fines.