Mercury ends up in the air through combustion processes in incinerators, coal fired power plants and other sources. This mercury then falls to the land and waters in the form of rain and snow. Mercury air pollution is much harder to track and control.
Airborne mercury can come from miles away, even across state lines.
States must address airborne sources of mercury across the state, and even in other states. The number of lakes and rivers that have unsafe mercury levels is far higher than for any other pollutant. There are thousands of lakes and rivers with mercury fish consumption advisories. States can use a special provision in the Clean Water Act, called a TMDL or a pollution reduction program, to set caps on the amount of mercury pollution that can enter a river or lake, regardless of where it comes from. Currently there is no proven or standard method for developing reduction programs for mercury, and they can be very expensive.