Fifty-five lakes in the Adirondack Mountains of New York were surveyed during 1982 for crustacean zooplankton, rotifers, phytoplankton, and water chemistry. The midsummer surface pH values ranged from 3.60 to 7.25. Lakes were selected in order to have a wide range of morphometry and watershed characteristics. Zooplankton species richness and diversity declined with pH. In lakes with pH less than 5.0, three species tended to dominate the growing season community. A discussion of the zooplankton communities in acidic lakes that have recently been treated with either agricultural limestone or sodium carbonate is included.