The white-clawed crayfish is in danger of being wiped out
Cumbria's rivers are being invaded by species which are putting native crayfish at risk, experts say.
Efforts are being made to prevent the spread of species such as the topmouth gudgeon and Chinese mitten crab, which are making their home in county rivers.
Cumbria has Europe's only stronghold population of white-clawed crayfish, at risk from American signal crayfish.
The South Cumbria Rivers Trust has appointed a specialist coordinator to come up with an eradication plan.
It is thought signal crayfish are finding their way into rivers such as the Kent and Duddon by visitors using boats or fishing equipment.
Signal crayfish are believed to have spread to the UK after being imported as a delicacy.
Rivers are also being hit by invasive plants like the Himalayan Balsam and Japanese Knotweed, according to the trust.
Bekka Close, of the South Cumbria Rivers Trust, said: "I have been working with invasive species for a number of years and they are notoriously difficult to eradicate.
"Given the high volume of visitors to the county and the movement of people around the lakes, there is an increased risk that new species could be brought into Cumbria on boats and equipment, making our task even more of a challenge."
She said work was under way to come up with a plan to tackle the invasive plants and fish.