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Lake acidification became an environmental issue of international significance in the late 1960s and early 1970s when Scandinavian scientists claimed that “acid rain” was the principal reasonwhy fish populations had declineddramaticallyin Swedish and Norwegian lakes (Oden, 1968; Jensen & Snekvik, 1972; Almer et al., 1974). Similar claims were being made at about the same time in Canada (Beamish & Harvey, 1972). However, these claims were not immediately accepted by all scientists. It was argued by some that acidification was due to natural factors or to changes in catchment land use and management (Rosenqvist 1977, 1978; Krug & Frink, 1983; Pennington, 1984).