An effort to rid a Highland loch of North American signal crayfish which are destroying the native wildlife is under way.
Signal crayfish have a voracious appetite and target frogs, young fish and their eggs when introduced to an ecosystem.
A month-long project has begun to eradicate the crustacia from the old Ballachulish slate quarry, near Fort William, and there are warnings that if they were to spread the impact on West Highland waters could be devastating.
Dr Colin Bean of Scottish Natural Heritage said: "Loch Ken [in the Borders] is a good example of a large water body which is infested with these animals and it is impossible to eradicate them so there is a real issue there as well.
"If they get into rivers where we have species of real conservation importance as well - such as salmon or fresh water pearl muscle - then they can have a negative impact not only on biodiversity, but on the economy as well."
The water is being treated with a chemical at a cost of £75,000 after the crustacia were discovered by chance.
Dr Diane Baum of the Lochaber Fisheries Trust said: "A Highland Council ranger was leading a group pond dipping. One of the children came along and said I’ve found this and it turned out to be a crayfish.
"The ranger was very well informed, knew what they were talking about and as soon as they saw it alerted SNH.”
Although the chemical being sprayed on the water is not harmful to humans, locals are being asked to stay away while the work continues.
It is a mystery as to how the crayfish ended up in the quarry, although some believe they were placed in the water to breed and be harvested for food.
Stewart Borland of Ballahulish Community Council said: "There’s no clues. It’s a bit of puzzle as to how it is only in one loch and not the other pool – although we are treating both.
"The best guess is it came in on a canoe or boat that’s been somewhere else and left it here."
This is the first time the species has been found in Lochaber. Locals and visitors are being asked to report any sightings of crayfish to the authorities.