"Advice" "Advice"

Help stop the spread of invasive plants and animals in British waters.

Invasive non-native species can have a damaging impact on British plants, animals and ecosystems – by spreading disease, competing for habitat and food and direct predation.

Plants that grow profusely can block waterways while some animals can damage riverbanks – so they also affect economic uses of our environment and add significant management costs.

As a water user, you may unknowingly be helping to spread invasive species from one water body to another in equipment, shoes and clothing.

Help stop this happening by following three simple steps:
Check, Clean, Dry.

Check your gear after leaving the water for mud, aquatic animals or plant material. Remove anything you find and leave it at the site.

Clean everything thoroughly as soon as you can, paying attention to nets, waders, and areas that are damp and hard to access. Use hot water if possible.

Dry everything for as long as possible before using elsewhere as some invasive plants and animals can survive for two weeks in damp conditions.

Top six invasive species

Look out for these in the river and riverbanks.

"Zebra Mussel"

Zebra Mussel, Dreissena polymorpha

The Zebra mussel is a sessile bivalve mollusc of typically 20 mm (max. 40 mm) length and brownish-yellowish colour with a characteristic dark and light coloured (“zebra”) zigzag banding.

It forms dense colonies attached to various hard substrates in both fresh and slightly brackish waters.

Can be found in both flowing and standing water bodies.

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"Killer Shrimp"

Killer Shrimp, Dikerogammarus villosus

Adults are up to 30mm in length. The body is curled and semi-transparent. They have two pairs of antennae and large, powerful mandibles. Newly hatched young are about 1.8mm in length and resemble adults.

While currently restricted, there are large areas of GB’s canals, rivers and lakes that would provide suitable habitat for the species. They require hard banks, slow flowing water and are salt tolerant so can also colonise brackish coastal habitats.

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"Signal crayfish"

Signal crayfish, Pacifastacus leniusculus

The signal crayfish is lobster-like in appearance and reaches a maximum size of 16-18cm. It is much larger than the native white-clawed crayfish and its claws have red undersides with a small turquoise/white blotch on the upper surface at the claw hinge.

Signal crayfish are found in streams, canals, rivers, lakes and ponds, and are also able to survive in brackish water.

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"Himalayan Balsam"

Himalayan Balsam, Impatiens glandulifera

Glabrous annual herb with stout succulent, reddish-translucent hollow stems to 2.5 m; leaves opposite or in whorls of 3, 5-18 cm long and 3-7 cm wide; flowers with short spur, helmeted upper petal, deep purplish-pink to white, strong balsam smell.

Moist and semi-shaded damp places, predominant on banksides by slow-moving watercourses.

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"Japanese Knotweed"

Japanese Knotweed, Fallopia japonica

Herbaceous perennial, with stems typically about 2m tall and an extensive system of rhizomes. It has large, roughly triangular leaves with truncate (not cordate (heart-shaped)) bases.

Disturbed habitats in urban areas, by water courses, canals and on waste ground, usually in full sunshine. It is shade tolerant and occasionally invades.

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"Giant Hogweed"

Giant Hogweed, Heracleum mantegazzianum

Aptly named ‘giant’, this umbellifer (member of the cow-parsley family) has flowering stems typically 2-3 m high bearing umbels of flowers up to 80 cm in diameter. The basal leaves are often 1 m or more in size.

It is especially abundant by lowland streams and rivers, but also occurs widely on waste ground and in rough pastures. It grows on moist fertile soils, achieving its greatest stature in partial shade. In more open grassland, flowering may be delayed by repeated grazing. It’s sap can cause severe skin burns.

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