MOST WANTED – Destructive Foreign Species That Are Destroying Our British Waterways
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Wed Aug 26, 2015 at 10:20am

MOST WANTED – Destructive Foreign Species That Are Destroying Our British Waterways

This is a list of the most wanted unwelcome visitors in the UK who have out stayed their visit to our British waterways. They have bullied their way into our beautiful waterways and are ruining the natural habitat for native species such as the water vole and the white-clawed crayfish to name but two native species that are affected by their unwelcome presence.

WANTED: Chinese Mitten Crab

ORIGINS: Southeast Asia

WHEREABOUTS: Mainly in London on the river Thames where they were first spotted over 70 years ago, Medway and Ouse. Also seen and recorded at other site throughout England and Wales, including the rivers Tyne, Tamar and Dee and Southfields Reservoir near Castleford, Yorkshire.

IDENTIFICATION: A large crab with a maximum carapace (body) length of 56 mm. Olive green in colour with paler legs, which are twice the length of the body. The most obvious distinguishing feature of the Chinese mitten crab is the dense mat of hair on the claws which look like mittens!

CRIME: Their extensive burrowing damages canals, drainage embankments and structures. Known to eat just about anything that crosses its path. It is also capable of leaving the water and crossing dry land to enter new waters.

IF SIGHTED: Contact the Environment Agency fisheries, who conduct regular trappings in an attempt to stop the spread.

WANTED: Red-Eared Terrapin

ORIGINS: Transported from the USA as pets during the Teenage Mutant Hero Turtles cartoon craze of the 1980s. They became a problem when released into the wild as unwanted pets.

WHEREABOUTS: The Midlands and Southern England sport the largest terrapin populations.

IDENTIFCATION: The average length ranges from 15 to 20 cm (6 to 8 in). The females of the species are usually larger than the males. They usually live between 20 and 30 years

CRIME: The waterways were a safer place for birds eggs and insect larvae before their appearance .

WANTED: American Signal Crayfish

ORIGINS: North America

WHEREABOUTS: Seen throughout England

IDENTIFICATION: 15cm-long beasts. They are bluish-brown to reddish-brown in colour with robust, large, smooth claws. They have a white to pale blue-green patch near the claw hinge, like the white flags that signalmen used for directing trains—hence the name.

CRIME: They are aggressive and breed faster than the native species. They also carry a fungal disease  ‘crayfish plague’ which is harmful to our native species. Lastly they are responsible for damaging the banks with their burrowing.

IF SIGHTED: Commonly caught in waterways of southern England using rod and reel. If caught signal crayfish must be removed from waterway and killed.

WANTED: Zander ORGINS: Eurasia

WHEREABOUTS: Found in slow flowing waters in Central England

IDENTIFICATION: It has a wide-mouth, excellent vision and fang-like teeth. Have an average length of 40–80 cm (16-32 inches) with a maximum length of 120 cm (47.25 inches).

CRIME: As a non-native predatory fish it has a big impact on other native coarse fish species.

WANTED: Zebra Mussels

ORIGINS: Eastern Europe. These stripey stowaways landed in Britain’s waterways on the hulls of ships from Eastern Europe and decided to stay.


IDENTIFICATION: Zebra mussels get their name from the striped pattern of their shells. However, the pattern varies greatly to where there are no stripes, only dark or light coloured shells. Zebra mussels can grow to a maximum length of about 50 mm (5-10 mm in the first year) and live four to five years.

CRIME: These nautical nuisances reproduce rapidly and form large colonies that attach to almost any submerged hard surface, impeding the smooth running of canal gates and sluices. They can spread easily as their larvae move through canals and rivers like cars on a motorway network. The invading mussels also kill British native freshwater mussels. If the zebra mussels get into water treatment works, they can block up the whole system.

WANTED: Sunbleak Fish

ORIGINS: Native to continental Europe but not the UK

WHEREABOUTS: Found in rivers and lakes throughout Somerset, Hampshire and also in Dorset.

IDENTIFICATION: A small fish, usually less than 9cm

CRIME:They compete with native species as they have similar diets and spawning areas, can be infected with parasites and are regarded as a pest to anglers.

WANTED: Topmouth Gudgeon


WHEREABOUTS: Found in waterways across England and Wales

IDENTIFICATION: I Measuring up to 9cms in length, the males are usually darker in appearance than the females. The interloper could pass itself off as a sardine in a identity parade CRIME: It breeds at four times the rate of native fish and it can also breed up to four times a year. Known to spread parasites and beating native species to food and habitat, it also eats the native fish’s eggs. It can breed up to four times a year.

IF SIGHTED: The Environment Agency fisheries staff conduct regular electro-fishing of affected waterways in an attempt to stop the spread and eradicate this fish. 

WANTED: Mink ORGINS: America

WHEREABOUTS: Throughout Britain’s waterways and can also spend time out of the water in urban areas.

IDENTIFICATION: Has brown or black fur and is between 30-60cm in length with a slender body and short legs. They are smaller than an otter.

CRIME: Initially brought to Britain in 1929 for commercial fur farms. Since the release into the wild during the 1950s they have breeding extensively in the wild.

SITUATION: Mink numbers have started to decline as our native otter population recovers. Otters are reported to attack and even kill mink which it seems is helping to reduce the numbers.