Water-quality data were collected from streams grenadine 35 basins in the southeaster-Ohio coal region to evaluate and categorize the effect of surface coal mining on stream quality. The study area is underlain by rocks of Pennsylvanian age, the most important coal-producing formations of which are the Allegheny and Monogahela Formations. The study area contains 276 data-collection sites, each of which was sampled four times over a 3-year period. Water and bed-material samples were collected. Each site was classified as 'abandoned,' reclaimed,' unmined,' or mixed,' depending on the proportion of the drainage basin disturbed by mining, and if mined, on the present condition of the mine. Of the 130 sites in the Monogahela Formation, 18 percent were classified as abandoned, 2 percent as reclaimed, 10 percent as unmined, and 70 percent as mixed. Of the 146 sites in the Allegheny Formation, 14 percent were classified as abandoned, 11 percent as unmined, and 75 percent as mixed. Streams draining the carbonate-bearing Monogahela Formation have a significantly greater buffering capacity than streams draining the Allegheny Formation. THere are significant differences in specific conductance; pH; alkalinity; acidity; hardness; total and dissolve manganese, and aluminum; dissolved nickel, zinc, and sulfate; and dissolved solids among mining-disturbance types in the Allegheny Formation. However, in stream draining the Monogahela Formation, only hardness, sulfur, dissolved solids, and dissolved manganese are significantly different among mining-disturbance types. Discriminant-function analysis of water-quality data was used to classify each 'mixed' site into one of four categories: Abandoned, reclaimed, unmined, or uncertain. In addition, observations in each of the first three categories were classified as strongly, moderately, or weakly characteristic of that category. The discriminant function was based on specific conductance, pH, acidity, dissolved sulfate, dissolved aluminum and dissolved manganese in streams draining the Allegheny Formation, and was based on specific conductance, dissolved sulfate, and alkalinity for streams draining the Monogahela Formation. Of the 'mixed' sites in the Monogahela Formation, 46 percent were reclassified as abandoned, 11 percent as reclaimed, 18 percent as unmined, and 24 percent as uncertain. One site was not classified because of insufficient data. Of the 'mixed' sites in the Allegheny Formation, 27 percent were reclassified as abandoned, 57 percent as unmined, and 15 percent as uncertain. Four sites were not classified because of insufficient data.