Sixty-five sampling sites, selected by a statistical design to represent lengths of perennial streams in North Dakota, were chosen to be sampled for water chemistry and mercury in fish tissue to establish unbiased baseline data. From the assessment of all water chemistry constituents, the percentage of stream length considered to be in poor condition was greater in the Rangeland Plains than in the Cultivated Plains. About 30 percent of perennial stream length in North Dakota was considered to be in good condition on the basis of mercury concentrations in fish tissue.