Lake District battles a killer from the suburbs: garden centre pondweed

The Lake District has declared war on an innocuous sounding plant, sold for £5 at garden centres, which is strangling life in three of the national park's finest treasures – Bassenthwaite Lake, Coniston Water and Derwent Water.

The Lake District has declared war on an innocuous sounding plant, sold for £5 at garden centres, which is strangling life in three of the national park's finest treasures – Bassenthwaite Lake, Coniston Water and Derwent Water.

The plant is a wild form of pondweed, which is native to New Zealand and difficult to kill. It was not recorded in Cumbria until 1986, but environmental surveys have now revealed it to be competing with native species such as floating water plantain – a rare plant which is in decline throughout Europe – and damaging the spawning areas of rare fish.

The plant's incursions have been helped by gardeners' traditional appreciation of it. Pondweed is one of a number of submerged aquatics that, by feeding off the dissolved mineral salts on which algae thrive, keeps garden ponds clean and oxygenates fish. Some of its rare forms were taken into consideration when one of Scotland's most popular rivers, the Tweed, was declared a Site of Special Scientific Interest two years ago.

But although pondweed's multiplication can be managed in a garden pond – where it takes root in the mud and sprouts leaves which float on the surface – shifting its wild forms from the lakes is almost impossible. This has led the Lake District National Park Authority and the Environment Agency to urge people not to buy it and to destroy it when removing it from ponds.

Phil Taylor, the park's senior ecologist, said: "There is no realistic way of getting rid of it from the three lakes, so it is absolutely vital that we prevent it spreading to other waters and we are seeking the help of the public to do this. We are also asking the public only to buy native aquatic plants for their ponds."

Anglers, sailors and walkers in the Lake District have been asked to clean their footwear, fishing tackle and boat propellers after use in an effort to curb the spread of the weed.

The warning is the second environmental threat to the Lake District made public in less than a month. Conservationists have said the character of the daffodil beds on the shores of Ullswater could change unless a more common variety is removed.

Although the wild species, Narcissus pseudonarcissus, is not threatened, it is already showing signs of turning into a hybrid.