More than a fifth of all species of freshwater fish in Britain face extinction and many others will become threatened unless urgent action is taken, according to a Government-funded study.
Several species had already died out this century, but the immediate concern should be for those rare and threatened species still in existence, fish biologists Peter Maitland and Alex Lyle said.
Their nationwide research, backed by the Nature Conservancy Council, showed that British native freshwater species face a number of difficulties.
Rivers and lakes had become repositories for enormous amounts of waste, ranging from toxic industrial chemicals to agricultural slurries and herbicides to domestic sewage.
Acid rain was being washed into water courses and as a result many rivers had become fishless, especially those in the industrial and heavily populated lowland areas of Britain. Many rivers were devoid of oxygen and comprised a lethal cocktail of various industrial chemicals, they said.
Barriers on rivers blocking the passage of migratory species, enrichment from farm fertilisers, overfishing and the introduction of new species had all contributed to the decline of native stocks, especially those of the rare and more sensitive species.
Some 55 species of freshwater fish have been found in Britain and at least 12 of these "urgently require specific conservation measures", said the biologists.
The burbot and the houting, a species of whitefish, had not been recorded for decades. Extremely rare species include the vendace, found in only two English lakes, the powan, found in only five or six sites including Loch Lomond, the pollan, resident in four Irish loughs, and the twaite and allis shad, the status of which was uncertain.
There were also a number of species which were not immediately threatened, but which had declined significantly in recent years, such as the Arctic char.
Britain had no nature reserves specifically for fish, said the biologists. There was an enormous amount of work to be done in the field of fish conservation.
