Last surviving British crayfish are hit by mystery pollution

One of Britain's last populations of native crayfish has come close to extinction after a mystery pollution incident.

One of Britain's last populations of native crayfish has come close to extinction after a mystery pollution incident.

Tens of thousands of the rare species were wiped out at the weekend in Hart Burn, near Morpeth in Northumberland.

The Environment Agency said it was the last population remaining untouched by the invasive American species which has been responsible for the demise of smaller native crayfish across much of England and Wales.

Ecologists spent the weekend surveying three kilometres of river after officers of the Environment Agency were called to the burn by a resident. Ecologist Anne Lewis said: "This is one of the largest populations of native crayfish in the UK and for them to be wiped out in this way is absolutely tragic. Hart Burn is one of the few remaining places where American Signal crayfish haven't threatened the native population, so this is a massive blow."

The four-inch native invertebrates are increasingly at risk from their larger and stronger cousin the American Signal Crayfish, which take over their habitat. American crayfish also carry "crayfish plague", which can devastate native populations. This makes areas where only native crayfish live even more important to their survival.

Environment Agency ecologists in the area yesterday were prepared to rescue surviving crayfish from the River Wansbeck, the northern stronghold of the species, but surveys showed no effects there.

It is estimated that the recovery of the population could take two to three years, as crayfish upstream should be able slowly to recolonise the affected area.

The Environment Agency said its officers were working hard to find the cause of the pollution.