Windermere took centre stage in a BBC Panorama investigation.
Water companies can make sewage pollution disappear from the official figures, the investigation claims.
Leaked records suggest United Utilities wrongly downgraded dozens of pollution events, the BBC show says – a claim denied by the firm.
The show, The Water Pollution Cover-Up, was broadcast at 8pm yesterday on BBC One and is available on the iPlayer.
“In more than 60 of these cases, the company appears to have wrongly downgraded the incidents to the lowest level, category four. They were all signed off by the Environment Agency.
“Category four incidents are not counted in published figures because they are supposed to have had no environmental impact. Only more serious categories one to three are counted.
“The Environment Agency guidance says category four should only be used where either pollution doesn’t get into the water course, or where it is of such insignificance that it doesn’t have an impact, for example a ‘trickle into a large water course’.”
But a spokesman for United Utilities said: “Panorama has made a series of allegations about United Utilities, which we strongly reject. Pollution incidents are investigated and action taken where necessary.
“The Environment Agency, as the regulator, determines both the initial and final categorisation of pollution incidents. We care passionately about the environment and the communities we serve and have just proposed an ambitious £13.7 billion investment plan – the biggest for over 100 years – to improve services for customers, communities and the environment here in the North West.”
Campaign group Save Windermere is featured in the investigation.
Headed by Matt Staniek, it is calling on the Environment Agency to reopen its investigation by December 18 into an incident where fish were killed last summer, because it argues the investigation was flawed.
Its overall aim is for the complete removal of all sewage discharges into the lake.
A spokesman said: “This requires United Utilities to commit to a long-term infrastructure investment scheme, which would ensure the protection of Windermere for future generations, thus protecting the local economy which relies on the lake.
“This follows case studies from around the world including Lake Annecy in France and Lake Washington in America, where complete removal was determined to be the most sustainable and environmentally friendly model, with benefits that outweigh the short term engineering impact.”
