Wastes, emissions, and discharges arising from farming activities. Causes include runoff and leaching of pesticides and fertilizers; pesticide drift and volatilization; erosion and dust from cultivation; and improper disposal of animal manure and carcasses. Some agricultural pollution is point source, e.g., large feedlots, which require permits under the Clean Water Act, but much is nonpoint source, meaning that it derives from dispersed origins, e.g., blowing dust or nutrients leaching from fields. As most pollution control programs have focused on particular categories of point sources, nonpoint and unregulated point sources account for an increasingly large proportion of remaining pollution. Based on state surveys, the Environmental Protection Agency concludes that agricultural sources account for over one-half the pollution impairing surface water quality in the U.S. The Clean Water Act mandates that states develop and implement management programs to control nonpoint sources of water pollution.