In the 1970s and 1980s, fish populations in hundreds of thousands of lakes in eastern North America and northern Europe were deteriorating.
While scientists speculated that sulfur dioxide and nitrogen emissions from coal-fired power plants were responsible, there was inadequate evidence to support this hypothesis. Whole-lake experiments at the IISD-ELA proved that acid rain, mimicked through the addition of sulfuric acid to lakes, resulted in dramatic impacts on lake food webs, including the collapse of fish populations. Changes were observed at acid concentrations much lower than those shown to be directly toxic to fish in laboratory studies. The findings strongly influenced emission control restrictions in the United States and Canada.