11 February 2007
Nearly 400 of Britain's most wildlife-rich lakes are being stifled by pollution, an official study has found. They include most of the country's best-known and best-loved expanses of water.
From the Lake District to the Norfolk Broads, from Scotland's Loch Lomond to Surrey's Frensham Great Pond, from wild Malham Tarn to suburban Virginia Water, they are being devastated, mainly by sewage and farming. Some, such as the haunting Semerwater in the Yorkshire Dales, are so badly affected that they are virtually dead.
The study, headed by the Environment Agency, covered the 1,047 "most ecologically valuable" of Britain's 14,000 lakes, those either protected as Sites of Special Scientific Interest (SSSI), or home to Britain's most endangered species.
It found that 379 of them are so "degraded" that they are in urgent need of "rehabilitation". It is now joining with other official bodies to mount a rescue programme of "lake habitat action plans".
"We all take lakes for granted," said Geoff Phillips, an Environment Agency ecologist who led the study. "Nonetheless, many of them are severely stressed as a result of human-induced pressures, to an extent inevitable on a densely populated island."
Historically lakes have received less attention in clean-up campaigns than rivers, but they are much more vulnerable because their more stagnant waters allow pollution to collect and do more damage.
Mostly they are being fed to death by sewage and - especially - wastes and fertilisers from agriculture. These cause weeds and algae to flourish, soaking up oxygen from the water and suffocating other life. And, partly as a result, they are often plagued by alien, invasive species.
Bassenthwaite Lake, in the north of the Lake District, exemplifies many of the problems. It is theoretically one of the most protected water bodies in the country - being designated under the EU Habitats Directive as an SSSI and as part of the Lake District National Park - and is Britain's main stronghold of a very rare fish, the slim, blue-green vendace. But it is still struggling to survive, despite efforts to rescue it.
For decades, it was overfed by effluent from a local sewage works; this has now been cleaned up, but phosphorous from the past pollution still lurks in its sediments. And it is still being contaminated by septic tanks used by houses around its shores.
More pollution comes from the droppings of the sheep that graze its catchment. And allowing too many sheep on to the fells make things worse; overgrazing erodes the soil, bringing it -and the wastes - down into the lake.
Trees are now being planted to help to stabilise the soil, but the waters produce blooms of blue-green algae, which can be toxic. And they encourage an invasive species - the Australian swamp stonecrop, originally introduced to Britain from Tasmania nearly 100 years ago - which smothers other organisms.
Windermere, to the south, is struggling against another set of perils. It, too, is polluted by sewage, augmented by a staggering six million visitors a year. It also receives run-off from cattle farming. Last year, its blue-green algal blooms were so bad that notices had to be put up warning people, and their dogs, not to go into the water.
It, too, has a rare fish - the cold-water Arctic char - but as pollution deprives the depths of the lake of oxygen in summer it is forced to swim nearer the surface in waters too warm for it to tolerate. Meanwhile, roach, an invasive species in this lake, flourish in the balmier temperatures brought by global warming.
The bonny banks of Loch Lomond similarly wash pollution into the lake from agriculture, and from fertilised golf courses - and it, too, is polluted by sewage.
Right across the country, the growth of algae is so bad that it has completely killed off underwater vegetation in many areas, which in turn destroys invertebrate life and leads to changes in fish populations. Some, such as Rollesby Broad and Cockshoot Broad, are being restored, but still suffer from past pollution. Others, such as Wroxham Broad, remain in deep trouble.
Surrey's Frensham Great Pond, tucked away in the Home Counties but with an ecology closer to lakes in the northern uplands, receives too many substances from earth disturbed by road building and other developments in its catchment area. By contrast, Malham Tarn, high in the Yorkshire Dales, has been damaged by nature lovers. A septic tank in a field studies centre on its shores polluted it for years; it has also been invaded by Canadian pondweed, probably brought on an angler's rod or a hiker's boots.
Perhaps the saddest story of all is at Semerwater in Wensleydale - which, by legend, covers a once-thriving city, cursed after turning away a poor man seeking food. It, said Dr Stewart Clarke, an ecologist at Natural England, has "suffered massive enrichment" from the dung of the cattle raised around it. As a result, he said, "virtually no submerged plants are left in Semerwater any more".
Norfolk Broads
Polluted by sewage. Phosphorous from sewage works remains in sediment
Frensham Great Pond, Surrey
Threatened by polluted soil disturbed by road building
Malham Tarn, Yorkshire Dales
Plagued by Canadian pondweed, probably introduced by anglers or hikers
Bassenthwaite Lake, Cumbria
Soil contaminated by sheep droppings has washed into the lake
http://news.independent.co.uk/environment/article2258886.ece
