Sewage flooding a river for hours was blamed on Anglian Water’s slow response to the incident.
The company has been fined £18,000 for failures at a pumping station near Peterborough that an investigation said showed up their “reactive attitude” to pollution.
District judge Ken Sheraton said Anglian Water should have given “a higher category of response” to a second sewage pump failing because the site at Yaxley was operating at a lower capacity with another pump already out of order.
The pumps were meant to regulate the flow of effluent but had stopped working a week apart, meaning raw sewage poured into Pig Water Drain for several hours and the damage was done before an engineer arrived at the pumping station in Windsor Road.
Investigators from the Environment Agency said at least 60 fish died with no chance of surviving the incident in February 2019. The final death toll was believed to be higher, with the fish killed by reduced oxygen and toxic ammonia in the water.
A dog-walker reported a creamy substance on the surface of the watercourse. The woman said she saw fish leaping from the water like they’d been electrocuted or attacked.