A species of mussels native to Ukraine has been found for the first time in the UK and experts are warning it could devastate British wetlands.
The Wildfowl and Wetland Trust (WWT) says it found Quagga mussels in the Wraysbury Reservoir near London Heathrow Airport last week.
The molluscs are less than 5cm long but breed so prolifically that their vast colonies can smother boat hulls, block pipes and potentially cause flooding.
They also have the ability to poison drinking water because they eat pollutants and then turn them into concentrated toxic faeces. This poses a risk to animals that use waterways as well as to humans.
The WWT also warned that the invasive mussels could "cost millions of pounds in tax and water bills to protect drinking water supplies".
The mussels are often spread by human activity, since they can attach themselves to the hulls of boats, fishing equipment and other hard surfaces.
The WWT's head of conservation policy, Jeff Knott, warns that all water users should take steps to avoid their spread: