Invasive Non-native Species

Non-native species have been introduced into the Uk for commercial or personal interests, but many have 'hitch-hiked'  via planes, ships and even people's luggage. Many are invasive creatures and plants which threaten native wildlife by eating native species, rapid breeding, damaging habitats or spreading disease. Many have no natural predators in the UK. There are more than 3,000 of these species, which cost our agriculture, horticulture and building industries an estimated £1.8bn every year.

What can you do?: Think about what you are growing in your ponds and gardens; never release anything into the wild; and report any invasive weeds or creatures that you see. Anglers and people with boats should also check, clean and dry their equipment to make sure they have no unwanted hitchhikers.

Here are the species do the greatest damage to our rivers and canals. If you want to help, contact the Canal & River Trust (canalrivertrust.org.uk), which is a charity that works to help control the threats to our native species and their environment.

Mink: Predators living in holes in the riverbank. The population of native water voles has fallen by 90% after mink escaped or were released from fur farms. Action:The Trust has been creating new habitat for watervoles across the country. They also monitor numbers of mink and supports targeted control of numbers.

Terrapins: Bought as pets but grow to the size of a dinner plate and are abandoned in waterways. They prey on dragonfly larvae, small fish and frogspawn, and even bully ducklings. Action:When found, these unwanted pets are taken to a rescue centre.

Giant Hogweed: Can grow up to 3m high, keeping native plants in the shade; in the summer each plant produces up to 80,000 seeds before it dies. The plant's toxic sap reacts with sunlight to blister your skin. The burns can be so deep that people have been hospitalised. The damaged skin then becomes hypersensitive to sunlight; a condition that can last for years. [If you do come into contact with the sap, cover the area to prevent the sap reacting with sunlight, and wash with soap and water.] It is an offence to cause this to grow in the wild under the Wildlife and Countryside Act 1981. Action: It needs to be removed professionally.  

Chinese Mitten Crab: Their pincers are coverred in fine hair, giving the appearance of mittens; they damage riverbanks by burrowing into them.

Japanese Knotweed: The bamboo-like weed can grow to 3m in just 10 weeks. It is so hardy it can burst through tarmac and concrete, causing costly damage to pavements, roads and buildings. It can grow from tiny fragments, and its presence can make a property unsaleable. Action:The Trust treats patches all over the canal network before small branches snap off and spread downstream.

Floating Pennywort: This fleshy stemmed plant was introduced to garden ponds in the 1980s. Now it infests watrerways, taking oxygen from fish and insects. It can grow from tiny fragments. Action: The Trust spends around £25,000 a year treating a single infestation of floating pennywort.

Killer Shrimp: These voracious predators were first spotted in 2010. They survive out of water for two weeks and spread from the Black Sea through commercial fishing. They prey on native shrimp, damselflies, water boatmen and smaller fish; and even kill prey and leave it uneaten.

Zebra Mussels: They degrade water quality and disrupt nature's balance. They rapidly form large colonies that attach to almost any submerged hard surface and gobble up the food supply. They also provide an ideal home for the killer shrimps, which have striped patterns to blend in with the mussels' shells. They are mostly spread through recreational boating and angling, when the mussels attach themselves to the hull and equipment and are then transported to other waters.

Himalayan Balsam: Introduced into gardens in 1839, this plant has pink orchid-like flowers. It has spread rapidly in the wild as its fruit pods can project the seeds several metres. Its impenetrable thickets bully out any other species and when it dies out in the winter it leaves riverbanks bare. Action: In June and July teams of volunteers organise balsam bashing parties to uproot the plants growing beside canals and rivers.

Azolla: This voracious water fern forms a dense blanket, which deprives other plants and animals of light and oxygen. Action: Large numbers of 2mm weevils originating from North America, like the azolla, are released and eat their way through the azolla in just a few weeks. The weevils don't eat anything else, so they don't damage native populations and once the azolla dies off, the weevils die off too. [Biocontrol is the use of a natural predator to control a pest. Any release of a biocontrol organism is carefully checked and tested to ensure there are no unforeseen or harmful results.]

Water Patrol (Canal & River Trust canalrivertrust.org.uk) April 2015