Mexico's top environmental official says a mining company lied about a spill of millions of gallons of acids and heavy metals.

Environment Secretary Juan Jose Guerra Abud says the mine falsely claimed the spill was caused by unusually heavy rain. Officials say a construction defect at a holding pond allowed mining waste to flow into two rivers and a dam downstream.

Guerra Abud says the Buenavista copper mine could face fines of up to $3 million for violations of safety and environmental standards. The mine is owned by the Grupo Mexico consortium.

National water commission head David Korenfeld says acids and pollutants like arsenic have been so diluted they are now within acceptable limits at a dam that supplies water to the capital of the northern state of Sonora.