Untreated sewage was pumped to Windermere after a disruption

The documents show that the pumps began discharging wastewater into the lake at 23:34 GMT and continued intermittently until 09:49 GMT the following day.

When the pumping station is fully operational, it will be permitted to discharge untreated wastewater into Windermere if it is flooded by rain or snowmelt. This was not the case in this incident, meaning the discharge of wastewater into the lake was illegal.

United Utilities insiders told the BBC that the emergency pumps operated at almost 500 liters per second for a total of six hours, discharging more than 10 million liters of raw sewage into the middle of the lake.

The water company says it has not measured the amount of untreated sewage pumped into the lake, but says the BBC’s estimate of the extent of the discharge is unreliable.

The company says the incident was “caused by an unexpected failure in the telecommunications network in the area, of which United Utilities was not informed.”

Windermere has suffered from algae blooms in recent summers, turning the water green and potentially toxic. The algae is caused by a buildup of phosphorus in the lake, caused in part by both treated and untreated sewage.

Findings from the February pollution incident indicate that United Utilities failed to take rapid and appropriate action to limit the amount of untreated pollution released.

Insiders at the water company told the BBC the company automatically received a notification about the error shortly after it occurred. They say if an off-hours crew had been dispatched to the site promptly, much of the pollution could have been prevented.

Instead, a technician arrived at the pumping station ten hours later and stopped the pollution shortly afterwards.

The water company must have known that a telecommunications failure at the pumping station would almost certainly result in wastewater being dumped into the lake. This happened in November 2022 in an almost identical incident, as reported by BBC Panorama.

United Utilities says it uses a risk-based prioritization process when deploying on-call teams. A spokesman said: “As soon as we discovered this fault was affecting the Glebe Road pumping station, our engineers took urgent action to resolve the situation.”

Matt Staniek from Save Windermere, which campaigns to end sewage pollution, told the BBC that sewage “remains the biggest threat to England’s largest lake”.

“Here in Windermere the same thing happens again and again: United Utilities pollutes the lake and the Environment Agency turns a blind eye to it.”

Equipment failures and pollution incidents such as this should be reported immediately to the EA so that it can assess and investigate the impacts.

Failure to notify the authority as soon as possible is a criminal offense under the site’s environmental permit.

But the EA did not receive the call until more than 13 hours after the telecommunications disruption and the pollution began.

An insider at EA told the BBC that it would be difficult to investigate the pollution if it was only reported after the incident.

“When these incidents are reported too late, it prevents us from witnessing the pollution and collecting evidence, and then we have to let them off with a slap on the wrist rather than the harsher sentences they probably deserve.”

United Utilities said it was only able to confirm that a spill had occurred at 12:30 GMT and that “the incident was reported to the Environment Agency within an hour of confirmation of the spill.”

The company also said it collected water samples near the site.

They appear to show that the wastewater release had limited or no impact on the lake. But they were collected more than four hours after the pollution stopped and were collected on the lakeshore, not in the middle of the lake where the wastewater was discharged.

Following the BBC Panorama investigation last year, the Environment Agency said it was tightening regulation, strengthening compliance controls and taking a new approach to “detect breaches and drive better performance from the water industry”.