Calls have been made to limit new developments near Windermere, in Cumbria, because of the threat of pollution to the lake.
Windermere Civic Society says the town's sewerage system overflows more than 200 times a year, spilling diluted waste into the lake.
The Lake District National Park Authority said all new developments must meet tough environment safeguards.
The Environment Agency said efforts would be made to reduce discharges.
Geoff Plunkett, vice chairman of the society, said: "It's not nice to have untreated sewage going into the lake. People swim in the lake and there are all sorts of water sports.
"We would like to stop the situation getting worse and then something be done about it.
"The infrastructure here has not grown at the same pace as development."
'Risk to bathing'
A spokesman for the Lake District National Park Authority, which is responsible for planning issues, said: "We would have real concerns if the water quality of Windermere was affected by any developments.
"But any development that does get approval would have to have some sort of environmental impact assessment done."
A spokesman for the Environment Agency said: "The discharge is dilute in nature and screened to ensure sewage debris is not discharged into the lake.
"However, we are concerned that the discharge load contributes to the overall nutrient load of the lake and presents and a risk to bathing water sites meeting their standards for water quality."
He said improvement works would be carried out between now and 2010 to limit the number of discharges.