A £3.6billion tunnel has been proposed to stop sewage being dumped into England’s largest lake.
The scheme, backed by water company United Utilities and environmental campaigners, aims to stop both raw sewage and treated wastewater being discharged into the lake.
Campaigners say nutrient-rich wastewater is contributing to the green algal blooms that have turned parts of Windermere a lurid colour during warmer months.
The proposals, known as Only Rainwater into Windermere (ORiW), would also connect 12,800 people to the sewage network for the first time.
But the huge project is not yet guaranteed to go ahead. The Government must decide whether the plans should be developed further and whether the £3.6billion price tag for the 12-mile tunnel is justified.
Sign up for all of the latest stories
Start your day informed with Metro's News Updates newsletter or get Breaking News alerts the moment it happens.
Windermere sits at the heart of the Lake District, a Unesco World Heritage site which attracts almost 18 million visitors every year.
The lake holds around 300 billion litres of water, and it can take up to nine months for water entering one end to travel to the other.
United Utilities chief executive Louise Beardmore described the proposals as a ‘100 year solution for this lake’.
She told the BBC: ‘In the UK we invest in five year periods and so we come along all the time and we do a bit, then we go away and we come back and do a bit more.
‘This is saying we need to do something differently.’
Beardmore said she was pleased that water companies, regulators, local authorities and environmental campaigners had joined forces to develop the plan.
Environmental activist Matt Staniek also welcomed the announcement, describing it as a ‘milestone’.
However, he warned that the proposal was only the beginning.
‘For me this is a plan on a piece of paper. It is not definitive action and that’s what I want to see,’ he said.
‘This is the beginning, and the end of this is the moment that sewage stops entering Windermere.’
Under the ORiW proposals, up to 86 miles of new sewage infrastructure would be built, alongside a single wastewater treatment works connected by a tunnel around four metres wide.
Two options are being considered for where the treated wastewater would go: one would discharge it into the River Leven, while the other would send it into the Irish Sea near Ulverston.
The report also sets out two ways the project could be funded.
One option would pass the cost on to United Utilities customers, potentially adding up to £3.17 a month to bills, depending on the route chosen.
But the Love Windermere group, which is linked to local businesses, wants the cost spread across England, increasing bills by up to 35p a month.
Group member Nigel Wilkinson said: ‘We believe Windermere is of such national significance and international significance that it is justifiable to treat this as a national asset and fund it accordingly.’
A Department for Environment, Food and Rural Affairs spokesperson said: ‘We share the public’s determination to protect this iconic lake.’
The department added that further work was needed to assess alternative options before a decision could be made.