Intensive studies by the USGS National Water-Quality Assessment (NAWQA) Project in agricultural areas provide insight into how agricultural activities have altered the natural flow of water and the way that agricultural chemicals enter streams and aquifers, and in particular how nutrients affect algal and invertebrate communities in agricultural streams. Agricultural chemicals move into and through every component of the hydrologic system, including air, soil, soil water, streams, wetlands, and groundwater. This web page provides an overview of USGS's research about agriculture and water quality. It includes related research, publications, and multimedia (Introduction).