Acidic lakes are found in many regions of the world and are especially common in those regions of the temperate northern hemisphere that have received high levels of acidic deposition during the last several decades. The National Lake Survey was a one-time fall sampling of lakes in regions of the United States suspected of containing lakes susceptible to acidic deposition. The sample lakes were statistically selected from all lakes identified on medium-scale topographic maps to permit population estimates to be calculated of the characteristics of lakes in the target populations in the regions surveyed. Acidic lakes were defined as those lakes with acid neutralizing capacity (ANC) < or = 0 (as determined by Gran analysis). This definition is limiting in that only the lakes with no remaining ANC are included. It is clear that lakes with ANC > 0 may be acidic based on pH; however, the rationale for defining other or additional categories of acidic lakes is beyond the scope of the presentation. (Copyright (c) 1988 E. Schweizerbart'sche Verlagsbuchhandlung.)