The Eastern Lake Survey-Phase I, was conducted in the fall of 1984 and involved a synoptic survey of water quality in a probability sample of 1612 lakes in 11 subregions in the eastern United States. In 1986, a subset of lakes in one subregion (Subregion 2B:Upper Peninsula of Michigan) were resurveyed to assess fish community status and concentrations of total mercury in fish tissue. In support of the National Acid Precipitation Assessment Program, 49 lakes were sampled over a 3-month period in summer 1986. Fish surveys were conducted by Michigan State University; total mercury samples were processed by Cornell University and analyzed by Syracuse University. The data base consists of four components: (1) water chemistry data for the 49 lakes collected in Fall 1984 during Phase I of the Eastern Lake Survey, (2) additional water chemistry collected during the Phase II survey in the summer of 1986, (3) the species and numbers of fish caught per unit of sampling gear, and (4) individual fish data on age, length, weight, and total mercury concentration.