The government is vowing to clean up Windermere and stop it being "choked" by sewage pollution.
Environment Secretary Steve Reed wants to ensure "only rainwater" enters England's largest lake.
On a visit to Cumbria on Monday as part of a Things Can Only Get Cleaner tour, Mr Reed said the government is working "to stop all sewage going into the lake and restore it to its natural beauty".
He added: "Windermere is a stunningly beautiful national treasure - but it's being choked by unacceptable levels of sewage pollution."
Mr Reed, who is meeting local campaigners, said Windermere had been contaminated with "more than 140 million litres" of pollution and the government is "committed to cleaning up this iconic lake" as part of its Plan For Change scheme.
The project aims to upgrade the crumbling water infrastructure and increase economic growth using more than £100bn of private investment - and Mr Reed said £200m had already been secured.
Local groups and organisations have set up a feasibility study to look into what is needed to eliminate sewage discharges into the lake, drawing on other examples from around the world.
Windermere, part of the Lake District National Park Unesco World Heritage Site, is home to more than 14,000 people.
The area's scenery, rare species and cultural heritage attract seven million visitors a year, generating £750m for the local economy.
Wastewater from United Utilities and private sewage treatment along with rural and urban land use are among a range of pollution issues it faces.
Sewage spills from water infrastructure have contributed to the pollution of beauty spots, including Windermere.
Storm overflows - which release untreated wastewater into rivers and seas when there is heavy rain to prevent sewers becoming overwhelmed - have dumped sewage into the lake.
Water utilities have been handed large fines for repeated and damaging illegal pollution in recent years and there is concern about the levels of leaks from water infrastructure.
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Last year, a protest was held outside the offices of United Utilities calling on the government to compel the firm to clean up the lake rather than pay huge dividends to shareholders.
Climate change and worsening weather extremes, from downpours to drought, are expected to pile more pressure on supplies.
(c) Sky News 2025: Government pledges to clean up Windermere sewage pollution