Fears have been voiced about the effects on fishing in the Borders after the discovery of a parasite
species of crayfish in the Tweed area.
The creatures are not native, like the White-clawed Crayfish
Environmentalists have warned the discovery of the American Signal Crayfish in the Ettrick Water is a serious threat.
The predators are said to devour the natural wildlife and wreck the ecosystem.
A study conducted in 1996 said Fishing pumps £13m into the local economy.
Experts believe fishing also supports more than 520 jobs which depend on the waters which are a Site of Special Scientific Interest.
The threatening crayfish is the first discovery of its kind in the Tweed area and efforts are being made to stop a "plague" from spreading.
It is against the law to keep the crayfish except under licence. It is not known how, when or where they got into the water.
They are dark brown or black crustaceans, alien to these shores and are highly destructive. They eat insects, frogs and juvenile fish and eggs, including salmon.
The predators also burrow into riverbanks and beds disrupting fish spawning grounds.
Scottish Natural Heritage's Janet Khan warned that the potential threat to Atlantic salmon and other native wildlife should not be underestimated.
'Risk to salmon'
She said: "This alien species also modifies rivers by removing aquatic vegetation, an important habitat for native species, and by burrowing into riverbanks.
"These crayfish can excavate huge amounts of soil every year and burrowing can cause damage to the river gravels in Atlantic salmon and trout spawning grounds, as well as causing increased erosion and destabilisation of river banks."
Nick Yonge, of the Tweed Foundation, said: 'It is particularly unfortunate that the Ettrick Water has been infected as this river is the spawning and juvenile ground for many of Tweed's spring salmon.
"It is absolutely essential that this pest is contained and, if possible, eradicated."