Somewhat alarmingly a population of North American Signal Crayfish have just recently been discovery by members of the Glen Nevis Ranger Service in the Ballachulish Quarry.
This is the most northerly confirmed population in the west of the country. The nearest previously known on the west was south of Oban. Most northern confirmed locations on the east coast are, flowing in to the Moray Firth, Rivers Lossie and Nairn.
Now an invasive species, ousting native species across Europe (carry a disease which affects native crayfish) the Signal Crayfish causes serious environmental damage, burrowing into river banks up to 1.5m, out-competing fish for shelter under stones and eating fish eggs & juveniles. Water users ~ incl. canoeists, kayakists and anglers should ensure thorough washing of equipment ~ esp. containers/boats following contact with waters containing known populations of this very damaging Crayfish.
For further guidance ref: http://www.canoescotland.org/access/Environment/Biosecurity.aspx