DENVER (AP) – A massive wastewater spill from an old gold mine in Colorado has prompted state officials to expand the list of downstream users they will warn after such accidents.

Last month, Colorado health officials notified only agencies inside the state after 3 million gallons of water tainted with heavy metals gushed out of the Gold King mine near Silverton and eventually reached the Animas, San Juan and Colorado rivers in New Mexico and Utah.

In the future, the Colorado Department of Public Health and Environment will warn downstream states as well, department spokesman Mark Salley said.

Colorado officials didn't know the magnitude of the spill when they issued their warnings, he said.

Officials in New Mexico were unhappy because they say the federal Environmental Protection Agency didn't alerted them when an EPA-supervised crew inadvertently triggered the spill about 70 miles from the New Mexico border.

The crew was trying to enter the mine as part of a cleanup operation and breached a debris pile that was holding back the water.

New Mexico officials first heard about the spill nearly 24 hours after it happened from the Southern Ute Indian Tribe, not the EPA, said Chris Sanchez, a spokesman for Gov. Susana Martinez.

The Southern Ute reservation straddles the Animas River in Colorado, and tribal officials had been alerted by the Colorado health department.

New Mexico officials contacted the EPA after hearing from the Southern Utes, Sanchez said.

"The EPA to this day has not been able to answer why the agency never contacted the state of New Mexico," Sanchez said in an email to The Associated Press.

EPA spokesman David Gray said he spoke to New Mexico's Environment Department about the spill at midday Aug. 6, a day after it occurred. Gray, who works in the EPA's Dallas regional office, said that was shortly after he learned about it.

New Mexico is part of a Dallas-based EPA region; Colorado is part of a separate region with headquarters in Denver.

The EPA has come under sharp criticism for causing the spill and for its handling of the aftermath. At least four congressional committee hearings are scheduled, starting Sept. 9.

The EPA's inspector general is investigating. The Interior Department, which is separate from the EPA, is also investigating, with the help of the Army Corps of Engineers.

EPA Administrator Gina McCarthy has said the agency accepts responsibility for the spill, calling it tragic and unfortunate.

The EPA has said water quality is returning to pre-spill levels. Colorado health officials said it is safe to eat trout from the Animas River.