Environment Secretary Steve Reed has pledged to ensure “only rainwater” enters England’s largest lake.

On a visit to Windermere in Cumbria he said the government was “committed” to the clean up as part of its Plan for Change scheme, which aims to upgrade crumbling water infrastructure using private investment.

Wastewater from water companies and private sewage treatment, along with rural and urban land use, are among a range of pollution issues the lake faces.

Reed said: “Windermere is a stunningly beautiful national treasure but it’s being choked by unacceptable levels of sewage pollution.”

Asked when the water in Windermere might be safe enough to swim in, he told BBC Breakfast: “It won’t be ready as quickly as summer. It’s taken a long time to get to the state that it’s in.”

Part of the Lake District National Park Unesco World Heritage Site, Windermere is home to more than 14,000 people and its scenery attracts an estimated seven million visitors per year.

But in 2024 it was revealed water company United Utilities repeatedly dumped millions of litres of raw sewage illegally into the lake over a three-year period.

Reed said it was “wholly unacceptable that this lake was allowed to be contaminated with so much pollution – more than 140 million litres.”

He said the government had secured an initial £200m to start work on diverting sewage away from Windermere and into treatment facilities to clean it up.

However, he warned the project would take time and further funding as part of its £100bn five-year plan across the water sector still needed to be secured.

“We are working with investors to bring that money in,” he said.

Matt Staniek, a campaigner against sewage pollution and founder of Save Windermere, said the announcement felt “like a new dawn” for Windermere.

“It’s phenomenal news – everyone should really appreciate this is big news for every single person in this country.”

He added this was a “first step” in their four-year campaign.

“This is so far just an objective, it’s a vision, it’s an ambition and we want to see this absolutely concrete.

“We want to see a legally binding commitment and we’re going to continue until that happens.”

Local groups and organisations – including Save Windermere, United Utilities and the Environment Agency (EA) – have set up a feasibility study to look into what is needed to eliminate sewage discharges into the lake from successful examples from around the world.

The government said a first step was to look at new methods to reduce pollution from private sewage discharges into Windermere.

These included new treatment plants, along with schemes which would let owners of septic tanks and package treatment works ask for a connection to the mains sewer under certain conditions.

As part of the scheme, United Utilities will invest £200m towards upgrading 10 wastewater treatment works at Windermere and reducing spills from storm overflows into the lake to 10 per year by 2030.

The environment secretary said there would also be 33 additional EA specialist officers in the region and a quadrupling of water company inspections.

Reed said: “The government is committed to cleaning up this iconic lake.

“That is why we are working with a range of local groups and organisations to stop all sewage going into the lake and restore it to its natural beauty.”