Land classification systems are useful for identifying areas of relative homogeneity among which attainable water quality varies according to predominant land type and present use. Five ecological regions in Ohio were delineated to evaluate a framework for assessing attainable water quality in small streams. Streams in relatively unimpacted, representative watersheds were selected in each region. Various water quality variables were sampled over a 16-month interval from July 1983 through November 1984. The highest water quality consistently occurred in the southeastern region; the lowest in the northwestern region. The correspondence between spatial patterns in water quality variables and the delineated regions, together with multivariate classification of the streams based on their major ion chemistry and nutrient richness, support the hypothesis that regional differences in attainable surface water quality occur and that a land classification system is useful for characterizing attainable water quality goals. Such a framework should be useful for planning, implementing, and monitoring pollution control programs.