Signal Crayfish
Pacifastacus leniusculus
Photo credit: Environment Agency
- Present in all the main rivers in the Yorkshire dales but not in all headwaters.
- Severe impact on white clawed crayfish which was widespread in the Dales until 20 years ago, populations have crashed due to crayfish plague (carried by signal crayfish).
Himalayan balsam
Impatiens glandulifera
Photo credit: GB Non-native Species Secretariat
- Widespread across the Yorkshire Dales, mostly near watercourses, largely absent from the moors.
- Outcompetes native flora by dominating riverbanks and increases river bank erosion.
Japanese knotweed
Reynoutria japonica
Photo credit: GB Non-native Species Secretariat
- Mostly absent from the Yorkshire Dales.
- Impacts native floral communities by creating dense ‘forests’.
Giant hogweed
Heracleum mantegazzianum
Photo credit: GB Non-native Species Secretariat
- Not present in the Yorkshire Dales but present at the periphery of the Park.
- Impacts on human health; its height and large leaf area forms a dense canopy out-competing natural, native vegetation. Overwinter die-back along riverbanks exposes bare earth resulting in an increased risk of bank erosion.
Grey squirrel
Sciurus carolinensis
Photo credit: GB Non-native Species Secretariat
Credit: Jeff Wilson 
Credit: Jeff Wilson 
Credit: Jeff Wilson
- Present throughout the Yorkshire Dales.
- Severe impact on red squirrel through competition and spread of by carrying and spreading squirrelpox virus.
New Zealand pigmyweed
Crassula helmsii
Photo credit: GB Non-native Species Secretariat
- On most of the catchments, and recorded in most of the reservoirs in the Yorkshire Dales. Not too widespread but likely underreported, present in the Washburn (Wharfe catchments).
- Displaces native plant species, reduces biodiversity, decreases water quality and flow, impedes recreational activities.