The U.S. Environmental Protection Agency (EPA) accidentally spilled about a million gallons of mustard-hued wastewater containing heavy metals into a Colorado river while investigating a leak at a mine, it said Thursday. Federal officials did not detect any health hazard following the spill.

According to the EPA, the spill happened Wednesday and wastewater flowed into the Animas river in San Juan County through a tributary. The sludge contained cadmium, aluminum, copper and calcium, the EPA said, according to the Associated Press. People were reportedly asked to stay out of the river and to keep domestic animals from drinking it.

EPA workers were using heavy machinery to pump and treat the wastewater at the time of the spill, EPA spokesman Rich Mylott said, according to Reuters.

"The primary environmental concern is the pulse of contaminated water containing sediment and metals flowing as an orange-colored discharge downstream," Mylott said.

The authorities said that the river was closed for recreational and other purposes, but maintained that water sources should be safe, according to reports. There was no harm to the aquatic life.

“The orange color is alarming to people, but that is not an indication in any way of a health risk,”Joan Card, an official with Region 8 of the EPA, said, according to the New York Times, adding that authorities are testing the river.

The wastewater flowed about a few hundred gallons per minute, according to Martin Hestmark, an assistant regional administrator with the agency, cited by the Times. Moreover, the EPA is reportedly deflecting the wastewater to treatment ponds it is building.

“We are very sorry for what happened,” Dave Ostrander, the director of emergency preparedness for Region 8 of EPA said Friday at a community meeting, the Denver Post reported. “This is a huge tragedy. It’s hard being on the other side of this. Typically we respond to emergencies, we don’t cause them.”