Water can become polluted by chemical, physical, or biological agents. Most water pollution in the United States is caused by nonpoint-source pollutants.
Groundwater pollution is difficult to clean up because pollutants cling to the materials that make up an aquifer.
Ocean pollution is mainly caused by coastal, nonpoint-source pollutants.
Government legislation, such as the Clean Water Act of 1972, has succeeded in reducing surface water pollution. Future challenges include reducing nonpoint-source pollution and groundwater pollution.
