The findings flatly contradict persistent government assurances that lake pollution in this country is minimal, and they raise the prospect that privatised water companies will have to fund a multi-million-pound clean-up.
The survey, carried out on behalf of the National Rivers Authority, now part of the Environment Agency, found that more than half our lakes are more than twice as dirty as they were 60 years ago, and nearly a third are more than three times more contaminated. Lakes thus join beaches and drinking water supplies as areas of environmental concern.
Among the worst affected are Windermere and Esthwaite Water in the Lake District, Loch Leven near Kinross, and the Norfolk Broads. Lough Neagh in Northern Ireland, the UK's largest lake, is badly polluted, as are Slapton Ley, the biggest lake in the South-west and Llangorse Lake in the Brecon Beacons.
For the privatised water companies this could mean another crisis, and for the Government it undermines a drive to minimise the action Britain has to take under a European Union directive to clean up our sewage works.
In all, Britain has more than 12,500 lakes larger than five acres, and perhaps as many as 300,000 bodies of standing water. The survey, by scientists from the Department of Environmental and Evolutionary Biology at Liverpool University, shows that 95.6 per cent of them have been significantly polluted by acid fall-out or nutrients, or both.
The acid - from burning oil, gas, and coal in homes, vehicles and industry - affects nearly three-quarters of the country's lakes. The nutrients - mainly phosphates discharged from sewage works and agriculture - damage nearly three-quarters of them and cause outbreaks of toxic algae.
Ministers have for years consistently denied that pollution is a widespread problem in lakes. In 1990, the then Junior Environment Minister, David Heathcote-Amory, said it was "limited to a small number of areas". The next year, ministers told a select committee it was "restricted to a few localised sites". And in March the Government's latest official report on the state of the country's environment was still saying that "the majority of UK waters" were "free" of the pollution.
During all this time official government advisory bodies were warning that the problem was both widespread and serious. Even a 1990 report published by the Soap and Detergent Industry Association, whose members were responsible for much of the pollution, concluded that it was "extremely common".
Professor Brian Moss, head of the team that carried out the survey, said yesterday: "Ministers want to say the environment is better than it is because the state of the environment reflects the state of their policies." He suspects that, in this case, there is another agenda - to try to evade an EU clean-up directive, which is only being implemented "to minimal effect" in Britain.
Much of the pollution comes from phosphates discharged from sewage works. The EU's Urban Waste Water Treatment Directive lays down that the phosphates must be removed if the effluent is being discharged into waters vulnerable to pollution.
This removal rarely happens in Britain, and ministers and the water companies took fright at the cost of a widespread clean-up, estimated at over pounds 740m. In 1994 the Government declared that only 33 of Britain's water bodies were vulnerable, requiring the extra sewage treatment. But Professor Moss says that all British waters should be classified in this way.
The new survey will lay the Government and the water firms open to prosecution in the European Court for failing to implement the directive, and this, in turn, could force them to spend huge sums cleaning up the pollution, as they have had to do following successful prosecutions over beach pollution.Reuse content