Some of the UK's most environmentally sensitive upland lakes and streams are recovering from the impact of acid rain, the government has said.
Greater use of natural gas instead of coal has led to a drop in acid rain
Acidic sulphur in Britain's water has generally halved in the last 15 years, the Department for Environment, Food and Rural Affairs said research showed.
In around half of 22 sites monitored by scientists, invertebrates and native algae were showing signs of recovery.
Environment minister Ben Bradshaw said the research was "encouraging".
It is thought that emissions controls and greater use of natural gas instead of coal is aiding the reduction and boosting fish, plants and insects.
Since 1970 there has been a 74% decline in sulphur dioxide emissions from 3.8 million tonnes to one million tonnes in 2002, and a 37% decline in emissions of nitrogen oxides.
These gases, along with emissions of ammonia from agriculture, are largely to blame for acid rain.
The wildlife and chemistry of upland lakes and rivers throughout the UK had also been severely affected.
Natterjack toads in the south of England may have died out due to the acidification of their spawning grounds, while salmon and trout fisheries in small Welsh rivers have also suffered significant declines.
The research, by University College London, is based on 22 of the most sensitive waters in the UK, which have been monitored continuously since 1988.
In some sites, acid-sensitive mosses and other aquatic plants were found for the first time in 15 years.
And at three of the most acidic sites identified, juvenile brown trout have recently been found for the first time since 1988.
Other examples of improvements include the River Etherow in the Pennines which has experienced substantial reductions in biologically toxic aluminium.
Also, the Round Loch of Glenhead, in Galloway, and Llyn Llag in Snowdonia - both with a well documented history of acidification - have seen stands of aquatic plants return.
Ben Bradshaw said the research highlighted how measures brought in by government were starting to bear fruit.
"It will take time for these sensitive waters to recover from the devastating effects of acid rain," he said.
"The switch from coal to gas in both power generation and in the home, while being mainly for economic reasons, has also meant a lot less pollution.
"New strengthened measures such as the implementation of the Large Combustion Plant Directive will help ease the situation even further."
Professor Rick Battarbee, of UCL, warned Britain's waters were not "in the clear".
"There is a long way to go. There is a risk that a wetter climate in the uplands in future might offset some of the recovery we are now seeing," he said.
"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."