Acid deposition clearly places severe stress on many ecosystems. Although the specific interactions of such deposition with Lake Fauna, soils and different vegetation types are still incompletely understood, acid deposition is known to have strongly in creased the acidity of lakes in Scandinavia, the northeastern U.S. and south eastern Canada, thereby leading to reductions in the size and diversity of fish populations. Such deposition also appears to play some role in the forest damage that has been discovered in parts of the northeastern US and Europe.