Environment: the top 10 public enemies in our waterways

The Environment Agency has released its ‘10 most wanted’ list of alien invaders – the plants and animals that are threatening to take over Britain’s waterways.

Invasive species now cost the UK economy an estimated £1.7billion every year.

They cause damage to riverbanks and buildings, increase flood risk, crowd out and kill off native wildlife and become so prolific on waterways that fishermen, boaters and anglers are unable to use them.

The cost of clearing land, such as construction sites, of invasive plants can run into the millions. The rise of invasive species is also a major challenge in meeting tough new EU targets on the ecology of rivers and lakes.

The Environment Agency already spends more than £2million a year controlling invasive species, and is aiming to increase funding to help more English rivers meet the new EU targets.

While Britain’s rivers are the healthiest for over 20 years and otters, salmon and other wildlife are returning for the first time since the industrial revolution, rivers that harbour non-native species could fall short of these tough new standards.

Trevor Renals, invasive species expert at the Environment Agency, said: “River water quality is the best its been since before the industrial revolution. But if we don’t control invasive species, we risk losing some of our precious native species and incurring even more clean up costs. We could also fall short of the strict EU targets for our rivers and lakes.

“The Environment Agency will be working with other environment bodies as well as community and volunteer groups to manage the spread of these damaging plants and animals.

“We would urge everyone to help stop the spread of these species by making sure that garden and pond plants don’t end up near rivers and parkland and thoroughly cleaning any fishing, boating and canoeing equipment when moving between waterways.”

The Environment Agency has the following 10 species on its hitlist:

1.Killer Shrimp

Dikerogammarus villosus is referred to as the killer shrimp as it has a voracious appetite. While only 3cm long, this tiny terror kills a huge range of native species such as freshwater invertebrates, particularly native shrimps and even very young fish, altering the ecology of the habitats it invades.

Insects such as damselflies and waterboatmen, common sights on British lakes and rivers, could be at risk, with knock-on effects on the species which feed on them.

The shrimp is currently found at three sites in England and Wales. The Environment Agency and its partners are working with anglers and boat owners to make sure that the species remains isolated in these locations and spreads no further.

2. Water Primrose

Creeping water primrose has recently been sold in the UK as a pond and aquarium plant. The plant can spread rapidly – taking over from all other wildlife, and completely covering waterways.

In France, Holland and Belgium this plant has caused serious damage to the aquatic environment and an economic study estimated that Ludwigia could cost the UK over £150 million a year if it were allowed become as well established here.

It has so far been recorded in sixteen sites across the UK. All of these infestations are either being managed, or have been eradicated.

3. Floating Pennywort

Floating pennywort was first brought to Britain in the 1980s and is still sold as a plant for aquariums and garden ponds.

It now grows in the shallow margins of slow-flowing water bodies (particularly ditches, slow flowing dykes and lakes), and forms dense interwoven mats of vegetation, which can often be mistaken for solid ground. These mats quickly cover the water surface, ruining the habitat for other wildlife and making sports such as boating canoeing and fishing impossible.

4. American Signal Crayfish

White clawed crayfish, which are native to the UK, are now seriously endangered, thanks to the spread of their cousins from across the pond – the much larger and more aggressive American signal crayfish.

American signal crayfish not only drive out native white clawed crayfish as they compete for food and habitat, but also carry a water-borne fungus which is fatal to our native species. It is predicted that white clawed crayfish could become extinct in the UK within decades if efforts are not made to protect them.

The Environment Agency is running the first ever captive breeding programme for native crayfish, releasing the new crayfish into ark sites where they are safe from American signal crayfish.

5. Topmouth Gudgeon

Originally from Japan but now found primarily here in stillwaters, the topmouth gudgeon can reproduce rapidly with numbers in excess of 65 fish per square metre. This tiny fish – which is only a few centimeters long – crowds out other fish, out competing them for food and can also introduce disease that prevents other species from spawning.

The Environment Agency is working to prevent the spread of topmouth gudgeon, and also eradicating them where they are found.

6. Giant Hogweed

Giant hogweed was introduced to Britain in 1893 as an ornamental plant. It escaped from gardens and now colonises many areas of wasteland and riverbanks.

The plant spreads rapidly along watercourses forming dense colonies that suppress the growth of native plants and grasses, leaving the banks bare of vegetation in winter and increasing the risk of erosion and flooding.

The stems, edges and underside of the leaves have small hairs containing poisonous sap, which can cause blistering and skin irritation.

7. Japanese Knotweed

Japanese knotweed was first brought to Britain in the mid-nineteenth century as an ornamental garden plant. Since then it has caused serious problems in a range of habitats – particularly roadsides, riverbanks and derelict land – by displacing native flora and even causing structural damage.

8. Himalayan Balsam

Himalayan balsam is a native of the western Himalayas. Introduced to Britain in 1839, it escaped from gardens and rapidly colonised river banks and areas of damp ground. It is the tallest annual plant in Britain, growing up to 3m high. The characteristic purplish-pink slipper-shaped flowers appear in June.

Himalayan balsam plants grow in dense stands that suppress the growth of native grasses and other flora. In autumn the plants die back, leaving the banks bare of vegetation, and therefore liable to erosion.

9. Mink

Mink are native to North America but were bought into Britain in the early 20th century to be bred for their fur. By the 1950s mink escaped from fur farms and spread throughout the country.

They usually hunt for food in woodlands and near watercourses and eat fish, small mammals and birds. They also prey upon poultry on farms and fish stocks in lakes. Mink often need to be controlled because of the damage that they can cause to wildlife, fisheries and property.

They are a particular danger to our native water voles, which are protected in this country. Currently mink are trapped and destroyed to minimise the damage they can wreak on our native species.

10. Parrot’s Feather

Parrot’s feather originates from l South America and is sold as a pond plant. It has now spread to over 150 sites in the UK.

The plants form dense mats that cover the water surface and can severely inhibit navigation, fishing and many other forms of water-related sport and recreation.

These dense mats cover the water surface, starving the waterbody of light, nutrients and oxygen which kills many of the species living in it and also increases the risk of flooding. They can also tempt children or animals to walk across it, exposing them to deep water.

The Environment Agency advises anyone who finds these plants in their garden or pond to visit the ‘be plant wise’ website for advice on how to remove and dispose of them.

The agency also urged river users to contact them immediately on 03708 506 506 if they suspect that they have seen killer shrimp in their local waterway.