Two keen-eyed anglers spotted the unusual shrimp on Friday 3 September and sent samples to the Environment Agency for identification. Once the shrimp was identified as possibly being Dikerogammarus villosus, precautionary biosecurity measures were quickly put into place.

The shrimp is a voracious predator (hence its common name of ‘killer shrimp’). It kills a range of native species – particularly native shrimps and even young fish – and this alters the ecology of the habitats it invades.

The shrimp can be as small as 3 mm but can grow up to 30 mm long, much larger than our native freshwater shrimp. Insects such as damselflies and water boatmen could be at risk, with knock-on effects on the species which feed on them.

The shrimp has spread across most of Western Europe over the past ten years and could have arrived at Grafham in a variety of ways, including boating, angling or naturally via birds.

Expert biologists are currently testing water entering and leaving Grafham to see whether the shrimp can be found in it. The results from this will indicate how widespread the problem might be and what measures need to be taken.

Dr Paul Leinster, Chief Executive of the Environment Agency, said: ‘We are devastated that this shrimp has been found in Britain, and very grateful to the keen-eyed anglers who found it. We are currently establishing the degree of the problem, and whether the shrimp is only in Grafham Water or if it is in nearby lakes and the Great Ouse as well.’

Grafham Water is a storage reservoir for water, but the shrimp poses no risk to drinking water supplies. If you think you have seen an unusual shrimp, please email a photograph to alert_nonnative@ceh.ac.uk for identification.