NAWQA assessments from 1988-1991 showed widespread detections of DDT and its breakdown products DDE and DDD in agricultural soils, stream water, suspended sediment, and fish in the Yakima River Basin in central Washington. Elevated concentrations of total DDT in bottom fish in the lower Yakima River were among the highest in the Nation. Repeated NAWQA assessments in the late 1990's showed that concentrations of DDT have decreased in fish such as large-scale suckers, smallmouth bass, and carp from the lower Yakima River by about half from the late 1980s. Decreases in concentrations have also been noted in stream water. These positive trends are most likely due to the implementation of best-management practices related to irrigation systems, cover crops and sediment retention basins that limit runoff of sediment and sorbed DDT.