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Tourism and water sports are making reservoirs hotspots for invasive species to thrive, according to South West Water.
Reservoirs, like Roadford Lake in Devon which is eight miles east of Launceston, has already seen a number of non-native species begin to out-compete other wildlife and dominate.
South West Water is warning people are unwittingly transporting species to lakes on their recreational equipment – like paddleboards – which have been used in other bodies of water.
Kate Hills, the biosecurity and invasives manager at South West Water, said: "American Signal Crayfish have been brought over here by humans and they out-compete our native wildlife.
"They eat them and they spread disease so they are not good for wildlife, they're not got for anglers and they're not good for water quality either.
"They create sedimentation and problems there."
The water services company is looking to curb the spread of invasive species and has introduced a wash-down station at Roadford Lake.
It is hoped visitors will clean their boats and other watercraft when they arrive and again before they leave to reduce the risk of transmission.
Kate added: "We have been bowled over at people's enthusiasm about wanting to protect their site, their wildlife and their hobby.
"It's keeping working with these people and particularly the new people who, since lockdown, are visiting sites for the first time and aren't sure what measures to take, getting them on board with what they can do too."
As well as non-native crayfish, there’s also Crassula, a New Zealand pygmyweed, which is prevalent at Roadford and is easier to transport by mistake.
Nick Baker, a naturalist, warns failing to prevent the spread of foreign fauna and flora can have a catastrophic impact on local wildlife.
He said: "They can be disastrous because they are not part of the system and they are generalists, they've got nothing to hold them back.
"They just have a party, an ecological party, and they go crazy.
"All it takes is a leaf of an invasive plant to be stuck in the cleats of your waders and you've set a problem, amok as it were."
Local populations of native white-clawed crayfish have been suffering in the Cinderford and Soudley Brook area of Gloucestershire because of a plague introduced by people.
'Check, Clean, Dry'
Lake users such as kayakers, anglers and stand-up paddle-boarders can help by remembering to Check, Clean, Dry:
Check – equipment and clothing for live organisms, particularly in areas that are damp or hard to inspect.
Clean – and wash all equipment, footwear and clothes thoroughly, using hot water wherever possible. If you come across any organisms, leave them at the water body where you found them.
Dry – all equipment and clothing, some species can live for many days in moist conditions. Make sure you don’t transfer water anywhere else.