The discovery of a rare blood-sucking fish in the River Wear is proof of high water quality, conservationists said.
Seven adult sea lampreys, which have toothed, funnel-like sucking mouths, have been found in the river near Chester-le-Street, County Durham.
Only three species of lampreys remain in Britain, and they are protected under European law.
The Environment Agency said the creatures only breed in water which is very clean.
So far the agency has identified twelve spawning sites, known as redds.
Source: BBC News.
