Water quality in the Trinity River basin, Texas, 1992-95

Water quality in the Trinity River basin was studied during 1992-95 as part of the USGS National Water-Quality Assessment (NAWQA) Program. Studies included chemical sampling of streams, streambed sediments, biota, and ground water; measuring distributions of biological communities in streams; and measuring physical characteristics of streams that affect biological habitat. The sampling design, in general, relates water-quality conditions to causative human and natural environmental factors. The occurrence of pesticides, for example, is related to land use. Trends are mixed, with a substantial improvement in the diversity of fish species downstream from Dallas and large decreases in regulated contaminants such as DDT; but increases in unregulated contaminants such as polychlorinated biphenyls.