Until the 1970s, federal and state laws did little to control the harmful water quality impacts of mining exploration, and mine wastes were regularly deposited wherever was convenient, including directly into streams. As a result, one enduring legacy of the boom and bust mining cycles in the United States from the mid-1800s to 1970 is widespread and unmitigated water pollution from inactive or abandoned mines. Uncontrolled pollution from inactive or abandoned mines contributes to the degradation of water quality in over 12,000 miles of rivers and streams in the United States and 180,000 acres of lakes and reservoirs.

Inactive or abandoned mines create water pollution when sulfur-laden mine waste rock or tailings piles mix with precipitation or surface water runoff. The mixture of sulfur-laden mine waste rock, water, and air creates sulfuric acid. The sulfuric acid from mine waste rock causes heavy metals in these rocks, such as zinc, cadmium, magnesium, and aluminum, to mobilize and leach into hydrologically connected waterways. This pollution is commonly referred to as acid-rock drainage or acid-mine drainage (AMD). Individual inactive or abandoned mine sites can disrupt ecosystems and threaten human health through contamination of drinking water supplies for thousands of years if left unremediated. In addition, the AMD creates acidic, or low hydrogenion concentration (pH), conditions in receiving streams.