The reduction follows the introduction of emission controls on industry and a switch to natural gas from coal for power generation.

Since 1970 there has been an 84 percent decline in UK emissions of sulphur dioxide and a 37 percent fall in nitrogen oxide emissions, the gases largely to blame for creating acid rain.

As a result, fish such as brown trout have begun to return to rivers and streams once polluted with acids.

The research, by University College London, studied records going back to 1998 for 22 of the most sensitive waters in the UK.

It found that in half of all sites, native algae and insects were showing signs of recovery.

Elsewhere aquatic plants have returned to lakes once badly hit by acidification, such as Round Loch of Glenhead in Galloway, Scotland and Llyn Llagi in North Wales.

"Wildlife in many of our upland lakes and streams in the UK has been badly affected by acid rain," said Professor Rick Battarbee of University College London .

"But following a major decrease in sulphur emissions there are encouraging signs of recovery, with newly hatched brown trout now re-appearing at the most acidic sites."

Local Environment Minister Ben Bradshaw said international cooperation was needed to maintain the reduction in pollution.

"It will take time for these sensitive waters to recover and, as the impacts of sulphur decrease, the impacts of nitrogen pollution from emissions become more noticeable.

"This is an issue without boundaries, so our focus must be on working closely with our European and international partners."