This information describes how human activities affect ground water and ground water recharge. After a discussion of point and nonpoint sources of contaminants, there is information about the effects of irrigation development, surface-water reservoirs, and removal of flood-plain vegetation on the interaction of ground water and surface water. The site also covers the effects of nitrogen use, pesticide application to agricultural lands, and atmospheric deposition on the quality of ground and surface water. All of the above are supported by illustrations. In addition, there is information about urban and industrial pollution, modification of river valleys including the construction of levees and reservoirs, and modification of the atmosphere, which includes atmospheric deposition and global warming.