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
The family of a businessman who was murdered in Worcestershire six years ago have renewed their appeal to find his body.
Wembley Stadium hosts the women's FA Cup final for the first time this weekend when last season's beaten semi-finalists meet
Evicted Tom Crawford has pleaded not guilty to a charge of assaulting a police officer outside his former home in Nottinghamshire.