The experimental acidification of a two-basin lake in northern Wisconsin is described. Background studies on the lake began in 1983, and the lake basins were separated by a vinyl curtain in August 1984; acidification of the north basin began in spring of 1985. Target pH values of 5.5, 5.0 and 4.5 are planned for two-year increments. Biotic and chemical responses and internal alkalinity generation are being studied. This report summarizes baseline studies on the lake, including acidification experiments in in situ enclosures (mesocosms), and lists predictions made by project investigators regarding responses of the lake ecosystem to acidification.