An alien invasion is silently creeping into Kingston under the waves of the River Thames, river conservationists have warned.

Asian clams, an invasive non-native species, were first found in British waters in 1998 in the Norfolk Broads and spotted in the Thames in six years later.

A 2007 study found the molluscs were “thriving in unprecedented densities in and around Ham on the River Thames”, they were restricted to the tidal part of the river downstream of Teddington Lock.

But Rebecca Law, project development officer at Thames Landscape Strategy, said: “We have noticed one of two in Kingston area, even as far as Molesey Lock, but we have not done any surveying on it.

“They take up the extra space and food so there is less space for our native species. It is more about space rather than competition. We are seeing a marked increase in alien species and a decrease in our own native species.”

Click here for more environmental news from greenguardian.co.uk