DURANGO — A spill that sent 1 million gallons of wastewater from an abandoned mine into the Animas River, turning the river orange, set off warnings Thursday that contaminants threaten water quality for those downstream.

The Environmental Protection Agency confirmed it triggered the spill while using heavy machinery to investigate pollutants at the Gold King Mine, north of Silverton.

Health and environmental officials are evaluating the river as it flows through San Juan and La Plata counties. They said the wastewater contained zinc, iron, copper and other heavy metals, prompting the EPA to warn agricultural users to shut off water intakes along the river and law officials to close the river to recreational users.

“There’s nothing that can be done to stop the flow of the river,” said Joe Lewandowski, a spokesman for Colorado Parks and Wildlife. “We can only wait until the flows slow down. We had a big heavy spring (of rain) here.”

Lewandowski said the EPA is testing to determine the river’s metal levels and results should be returned by mid-Friday.

Downstream in Durango, hundreds of people gathered along the Animas River to watch as the blue waters turned a thick, radiant orange and yellow just after 8 p.m., nearly 34 hours after the spill started.

“It is a sad day. The fish could be gone,” said Daniel Silva, 37, who was fishing near Durango as he does every day after work. “I am safety-orientated. Working in the oil fields, we take measures every day to prevent leakage. Why didn’t they? If this kills the fish, what do we do?”

After people told him the contamination was coming, he stopped fishing, and his daughter, who was swimming, got out of the water. And they waited on a bridge.

City officials asked residents to cut back on their water use, and irrigation of city land at Fort Lewis College was stopped.

The La Plata County Sheriff’s Office has closed the river from the San Juan County line — including Durango — to New Mexico. Authorities say they will re-evaluate the closure once the EPA tests are confirmed.

The spill was triggered at 10:30 a.m. Wednesday at the mine on the upper portions of Cement Creek, about 55 miles north of Durango. The fluid was being held behind unconsolidated debris near an abandoned mine portal, the EPA says. The agency called the release “unexpected.”

Deputy Stephen Lowrance of the San Juan County Sheriff’s Office said authorities are keeping people away from the Animas. In Silverton, signs have been posted warning of the danger, and the sheriff’s office sent out a public health advisory to stay away from Cement Creek and the Animas River.

“The river looks pretty nasty,” Lowrance said. “It doesn’t look like water; it just looks like sludge.”

The mine is owned by Golden-based San Juan Corp., Durango attorney Nancy Agro said Thursday afternoon. She said the EPA had been operating at the site for years under an access agreement.

“Upon suspending work last year, the EPA backfilled the portal to the mine,” Argo said in a statement. “On (Wednesday), while the EPA was removing the backfill from the portal to the Gold King Mine to continue its investigation this year, the plug blew out, releasing contaminated water behind the backfill.”

At the time of the spill, EPA responders were at the scene evaluating the toxic materials already leaking into Cement Creek.

“There were several workers at the site at the time of the breach. All were unharmed,” the San Juan Basin Health Department said in a news release. “The EPA recommends that recreational users of the Animas River avoid contact with or use of the river until the pulse of mine water passes.”

Pet owners have been told to keep their dogs and livestock out of the Animas River until testing is done.

Steve Salka, utilities manager for the city of Durango, said he pulls water from the Animas in the summer to help replenish the Terminal Reservoir. He said that although the city’s main water source is the Florida River, the contamination could cause serious problems.

“I want to know what’s in it,” he said Thursday. “The most important thing is what’s in it. I need to know.

“Back in the 1800s, things were used in mining that aren’t allowed anymore.”

The Animas is a 126-mile river that flows into the San Juan River in Farmington, N.M. The San Juan eventually spills into the Colorado River in Utah.

Todd Hartman, spokesman for the state’s Department of Natural Resources, says the mine operated more than a century ago. It was permitted again in 1986 but never produced in the modern era, he said.

“Its permit was revoked in 2005,” he said.

Bill Simon, one of coordinators for the Animas River Stakeholders Group, a water-quality collaborative, said the Gold King Mine was one of several abandoned sites in the area they have been monitoring for decades.

“I think the EPA may have misinterpreted what was going on,” Simon said.

Simon said iron oxide in the spill is his biggest concern, especially since it can clog the gills of fish and large invertebrates.

“This river system is somewhat used to pretty poor water quality anyway, so it remains to be seen what effect it’s going to be on aquatic life,” he said.

The EPA agrees and says because of long-standing water-quality impairment associated with heavy metals in Cement Creek, there are no fish populations. Further, federal officials say, the Animas River historically has been impaired for several miles downstream of Silverton.

It’s unknown whether the spill could have any human health impacts, officials say.

“We are monitoring the situation very closely and working with the EPA to get testing results to make sure we minimize any health impacts,” said Flannery O’Neil, spokeswoman for the area’s health department.

Colorado Parks and Wildlife says it is monitoring wildlife health in the area.

The agency has placed cages with fish in the river to see how they react to the waters. Officials say they should know Friday whether there were any effects.

“This is a significant spill,” said Elizabeth Holley, an assistant professor of mining engineering at the Colorado Schools of Mines.

Staff writer Yesenia Robles contributed to this report.