"Killer Shrimp" are among the worst alien invaders of Britain's waterways, which officials say are costing billions of pounds to tackle.
As well as introduced animals, several species of pond plants which have escaped from gardens and parks are also on the list of non-native flora and fauna posing a threat to the country's rivers and lakes.
According to the Environment Agency, the intruders cost the UK economy about £1.7bn a year, damaging riverbanks and buildings, increasing flood risk and harming native wildlife.
The worst offender, according to the Environment Agency, is the killer shrimp which, despite being just 3cm long and, so far, restricted in its range, has a voracious appetite and kills a huge variety of native species such as shrimp and young fish, altering the make-up of habitats it invades.
Other creatures on the most wanted list include the American signal crayfish, the topmouth gudgeon and the mink, which preys on native water voles.