Wildlife boom shows that rivers are cleaner

The Government agency, which regulates the use and management of rivers and plays a role in looking after their habitats, said water quality in English and Welsh rivers had improved year-on-year for the past 20 years.

Several wildlife species have benefited, including otters that were hit by the effects of pesticides but are now found back in every region in England and Wales.

But conservationists warned that almost three quarters of rivers fall below tougher new European standards because they do not support the wildlife which should be found in them.

The Environment Agency said the Thames, which this year won the world's biggest environmental prize after the once "biologically dead" river was restored to life, saw record numbers of sea trout in 2010.

And the River Tyne has seen the most migrating salmon since records began.

The water vole, immortalised as Ratty in Wind in the Willows, has suffered a dramatic decline since the 1990s as a result of loss of river habitat and predation by mink – but the Agency said its latest survey had revealed more than 30 hotspots where the mammal has strongholds or made a comeback.