"Killer shrimp" top the list of the 10 worst alien invaders of Britain's waterways which officials say are costing billions of pounds to tackle.
Several species of pond plant which have escaped from gardens and parks are also on the "most wanted" list of non-native wildlife which pose a threat to the country's rivers and lakes.
According to the Environment Agency, invasive species cost the UK economy around £1.7 billion a year, causing damage to riverbanks and buildings, increasing flood risk and hitting native wildlife. They can even become so prolific that anglers, fishermen and boaters cannot use the waterways.
The worst offender, according to the Environment Agency, is the killer shrimp which, despite being just 3cm long, has a voracious appetite and kills a huge range of native species such as shrimp and young fish, altering the make-up of habitats it invades.
Other creatures in the 10 most wanted list include the American signal crayfish which has endangered our native white-clawed species, the topmouth gudgeon fish which hits other species, and the mink, which eats water voles.
The harmless-sounding water primrose, the floating pennywort and parrot's feather are pond plants which have spread into the environment, clogging up and damaging water habitats.
Giant hogweed, Japanese knotweed and Himalayan balsam are all taking their toll on riverbanks and other areas, with the hogweed containing a poisonous sap, the knotweed causing structural damage and all three suppressing native plants and causing soil erosion.
The invasive species could hamper efforts to improve the quality of rivers to meet tough new EU targets, the Environment Agency warned. It is already spending £2 million a year controlling invasive species, and will be increasing its efforts with partners such as government conservation agency Natural England.
Trevor Renals, invasive species expert at the Environment Agency, said: "River water quality is the best it's 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."