Invasive non-native species are one of the greatest threats to biodiversity in the UK.

So the discovery that signal crayfish – one of the most problematic of all invasive non-native species in the UK – had recently colonised Dalbeattie Reservior near Dumfries was a cause for concern for the reservoir’s owner, Scottish Water.

Particularly as the reservoir and the surrounding Urr Water catchment are popular with the public, including for angling.

Background to the project

Brought to the UK from North America, signal crayfish reproduce and spread rapidly. They out-compete native species for food, with potentially devastating impacts on local biodiversity.

The risk of the signal crayfish spreading from the reservoir into the surrounding rivers and streams was considered very high. This raised the potential of a catastrophic impact on the aquatic ecology downstream of the reservoir and in particular on an important salmon fishery nearby.

Both UK and European legislation mean that water companies and others have a requirement and responsibility to avoid the spread of invasive non-native species and, where possible, to control existing populations.

Scottish Water therefore wanted to act quickly to address the problem.

What we did

APEM field scientist holding signal crayfish


Scottish Water asked APEM to carry out a feasibility study looking into the potential to eradicate the crayfish from the reservoir.

This was completed in March 2016 and the program was subsequently licensed and consented by Scottish regulators and the HSE for application later that year.

APEM then worked closely with Scottish Water, the Scottish Environment Protection Agency, Marine Scotland Science, Scottish Natural Heritage, the Galloway Fisheries Trust and the Dalbeattie Angling Association to determine the best way to carry out the eradication program.

Further advice was sought from global specialists in the field of crayfish colonisation and invasive species control.

In August 2016 the reservoir was drawn down and isolated and then treated with a natural biocide. Dosing of the reservoir used a range of bankside and floating equipment.

Extensive measures were taken to protect all animals in the surrounding catchment, while public access to the site was also controlled to ensure no hazard to the general public.

Over the following eight weeks the water in the reservoir was tested using bioassays to establish the concentrations of biocide remaining in it. In addition, crayfish surveys were undertaken in and around the reservoir to ascertain the efficacy of the treatment.

BG Shape 5 - Wave


  • By November 2016 the signal crayfish population had been eradicated and the risk to the Urr Water catchment eliminated
  • With the threat from signal crayfish eliminated the aquatic ecology of the site is once again thriving
  • The public were allowed to return to Dalbeattie Reservoir
Dalbeattie Reservoir, while on signal crayfish survey

GB Non-native Species Secretariat: ID and guide