The Wetlands and Wildfowl Trust (WWT) based at Slimbridge in Gloucestershire has warned that an invasive and dangerous species of mussel has been found in British waters.
And scientists are saying that it may already have been joined by other invasive species of shrimps.
The Quagga mussel originates in the southwest of Europe from around the Black Sea and the Caspian Sea.
It was found last week for the first time in the UK in the Wraysbury River near Heathrow airport, a river which feeds The WWT's London centre at Barnes.
The mussels are less that 5cm long but they breed prolifically and from colonies on hard surfaces that can damage boat hulls, block pipes and cause flooding.
In the United States infestation by the mussels threatens to shut the Hoover Dam and cut of the Las Vegas water supply.
Jeff Knott, head of Conservation for the WWT, which was founded in Gloucestershire, said: "This is a worrying, but entirely predictable, development that could be devastating to British wetlands.
"Quagga mussels are likely to indirectly cause suffering and death for hundreds of thousands of native animals, fish and plants and cost millions of pounds in tax and water bills to protect drinking water supplies.
"These tiny mussels can be devastating but look so innocuous, which is why it's so difficult for boaters, anglers and other water users to avoid accidentally transferring them between water bodies when they latch onto their equipment.
"That's why it's so important for all water users to remember the motto "clean, check, dry" when they pack up their equipment to help slow the spread.
"Quagga mussels are a prime example of why we need stronger controls on invasive species being brought into this country.
"Prevention is far cheaper and more effective than trying to control an infestation that's already established.
"There are plenty of other dangerous potential invasive species.
"Quagga mussels may have arrived, but we need to protect the UK against the next invasive species."
And scientists are warning that shrimp species also from the Caspian region like the demon shrimp (Dikerogammarus haemophabes) and killer shrimp (Dikerogammarus villosus) are likely to be in the country already, though they have not been detected. The quagga mussel was named as the greatest threat to native wildlife of any alien species by scientists this year.
Anyone who finds a suspected quagga mussel should report it at Quagga mussel
