Soaring nitrate and phosphate pollution across a legally protected area of the Lake District has led to Natural England raising the alarm.
The River Derwent and Bassenthwaite Lake Special Area of Conservation has officially been found to be in an unfavourable – or deteriorating – condition.
Water qualities are being damaged by exceeded nutrient thresholds, caused by human activity such as soaps, shampoos and detergents, as well as farm run-off.
The problem can cause important wildlife and habitat sites to be overcome by plants and algae, as well as gobbling up all the oxygen in water and leaving it unable to support other life.
The local catchment is home to threatened butterflies, rare lampreys, Atlantic salmon and otters, among others, and consists of standing and running water courses, bogs, marsh and woodland.
The lake, along with Derwentwater, also supports Britain’s rarest freshwater fish – the vendace – which is now extinct in Scotland.
Natural England, the Government’s adviser for the natural environment, has now written to the Lake District National Park Authority about the matter and the authority is setting up a project board to address the problems.
Local authorities including Allerdale Borough Council and Copeland Borough Council have also been alerted.
Natural England said tourism attractions and accommodation frequently generate additional wastewater and can cause “nutrient overloading”.
The work by the LDNPA will mean a fresh look at the catchments to enable pollution issues to be understood, strategies for restoring habitat sites and mitigation solutions.
Sections of the River Eden are also part of the warning, with Carlisle City Council the lead authority. Other affected sites in Cumbria include the River Kent in Kendal and Esthwaite in the south Lakes, although it is a nationwide issue.
Such is the concern about elevated nutrients in water courses that some planning applications – such as new homes or tourism accommodation – can be refused if it makes the problem worse, although built-in mitigation measures can see developments given the green light.
Dozens of local authorities around the country are receiving similar warnings from Natural England.
The Department for Levelling Up, Housing and Communities is said to be providing £100,000 per affected catchment to tackle the issue. National park members sitting this week will be updated about the issue.