The wastewater came from the Buenavista copper mine in Cananea, Mexico, situated only about 25 miles from the U.S. border, and contaminated the Bacanuchi River, a tributary of the Sonora River. The spill affects seven different municipalities, including the state capital of Hermosillo, which has a population of nearly 800,000 people, although the river is not a major water source for the capital.
PROFEPA, Mexico's federal agency charged with environmental protection, is monitoring water quality at multiple points along the river and has already ordered that the company, Buenavista del Cobre, part of the mining giant Grupo Mexico, provide "full remediation" for the spill.
The state of Sonora is Mexico's leading producer of gold, copper, and graphite.
In 2009 an American subsidiary of Grupo Mexico, Asarco, payed the U.S. government a record $1.79 billion to settle hazardous waste pollution in 19 U.S. states.