According to the Department for the Environment, Food and Rural Affairs (DEFRA), non-native invasive species can prey on, compete with and displace native wildlife. The can spread disease and block waterways. They can completely alter the balance of ecology in a water system.
Fish populations can alter, and they can block up waterways which mean boat users have to take different routes. The financial costs can run into millions of pounds.
More top news
An ITV News investigation has uncovered the staggering scale of disruption caused by over-running roadworks across the country.
Police are concerned for the safety of two teenage boys, who were last seen catching a train catching a train to Sheffield.
Divers have recovered 10 First World War mustard gas bombs from the bottom of a lake.