Non-native Crayfish Introduction and Impact in UK Waterways

By the Editorial Team · Friday, September 18, 2026

Non-native crayfish species, especially the American signal crayfish, have become established in UK waterways, outcompeting the native white-clawed crayfish and spreading a fatal disease known as crayfish plague. This invasion threatens native populations and damages aquatic environments, complicating conservation efforts and requiring regulated control measures to prevent further spread.

The United Kingdom’s waterways are home to a number of non-native crayfish species that have increasingly impacted native populations and aquatic ecosystems. The only crayfish species native to the UK is the white-clawed crayfish (Austropotamobius pallipes), but several foreign species have been introduced over recent decades, primarily through escapes from aquaculture and aquarium releases.

The most significant invasive species is the American signal crayfish (Pacifastacus leniusculus), which has established itself in various English rivers and lakes since escaping from commercial farms in the 1960s and 1970s. The species derives its name from a distinctive white marking between its claws, which is thought to be a signaling feature. Signal crayfish are larger and more aggressive than the native white-clawed crayfish, leading to competitive displacement across several habitats.

A critical concern with the signal crayfish is its role as a carrier of crayfish plague, a disease caused by a water mold that proves fatal to the native white-clawed crayfish but does not affect the American invaders. This has exacerbated the decline of the indigenous species, mirroring challenges faced by other native wildlife when invasive competitors are introduced.

Additionally, signal crayfish are omnivorous and known to burrow into riverbanks, causing erosion and damage to aquatic environments. Despite being edible, signal crayfish have not gained significant popularity in local cuisine. Their darker coloration may be a factor, although they turn red or pink when cooked, similar to lobsters. Cultural hesitancy toward eating freshwater crustaceans also contributes to the limited culinary use of these crayfish. Regulations require individuals who catch signal crayfish to have a license, aimed at preventing their further spread through human activity.

Besides the signal crayfish, other non-native species present in UK waterways include the spiny-cheek crayfish, the virile crayfish, the noble crayfish, and the narrow-clawed or Turkish crayfish, all listed by the Environment Agency. Some of these species may also be vulnerable to crayfish plague, which could influence their long-term presence.

Efforts to manage the expanding populations of non-native crayfish face significant challenges, and the presence of species like the signal crayfish appears to be a permanent feature of the UK’s freshwater ecosystems.

This article was reported by synthesizing coverage from multiple independent news outlets to present a balanced, unbiased account. Read about our editorial standards. Spotted an error? Let us know.