Acidic wastewater from an abandoned mine above Silverton coursed its way through La Plata County on Thursday, turning the Animas River a golden-brown, forcing the city of Durango to stop pumping raw water from the river, and leading the sheriff to order a closure of the river to public use.

Residents lined the banks of the Animas River on Thursday afternoon to watch the toxic wastewater as it flowed through Durango city limits.

A mining and safety team working on behalf of the Environmental Protection Agency was investigating contamination at the mine and triggered the release, according to a news release issued by the Environmental Protection Agency.

The accident occurred about 10:30 a.m. Wednesday at the Gold King Mine in San Juan County. When the accident happened, EPA’s team was working with heavy equipment to secure and consolidate a safe way to enter the mine and access contaminated water, said Richard Mylott, a spokesman with the EPA in Denver. The project was intended to pump and treat the water and reduce metals pollution flowing out of the mine into the Cement Creek watershed, he said.

The mishap released about 1 million gallons of acidic water containing sediment and metals flowing as an orange-colored discharge downstream through Cement Creek and into the Animas River.

EPA officials said testing will begin the water Friday to determine the extent of the damage and the exact contaminants.

The Animas River was closed to tubers, rafters and swimmers Thursday beginning at 3 p.m., said Lt. Brandon Tisher, with the La Plata County Sheriff’s Office. The closure will remain in effect indefinitely until the river is deemed safe, he said. Government officials aren’t certain what toxins and at what levels they are present in the river coming downstream, and, therefore, decided it was best to close the river to public use.

The closure, which applies to all flotation devices, is in effect for the entire stretch of the Animas River in La Plata County.

“This decision was made in the interest of public health after consultation with the Environmental Protection Agency, the Colorado Department of Health and Environment, San Juan Basin Health Department and representatives of the Southern Ute Indian Tribe,” said Sheriff Sean Smith in a news release. “This order shall remain in effect until it is determined that the river is safe. EPA test results of the Animas River are expected within 24-48 hours, and the order will be re-evaluated at that time.”

City residents are being asked to conserve water for the next few days.

The city of Durango stopped pumping water out of the Animas River on Wednesday to make sure none of the waste could be sucked up into the city reservoir.

The Animas is an important secondary source of water for the city during the summer, and residents need to conserve as much water as possible over the next few days until the water in the Animas is safe to use, said Steve Salka, the city’s utilities director.

During the emergency, Salka is not going to be sending raw water to Fort Lewis College or Hillcrest Golf Course. The city also will not water any city-owned parks for the next three days to help conserve, he said.

On hot summer days, the city can use up to 9.2 million gallons a day. But the city can pump only 5.3 million gallons a day out of the Florida River, the city’s primary source of water.

The city reservoir was about 4.5 feet below capacity on Wednesday, Salka said.

“This couldn’t happen at a worse time for me, so I have to be really cautious,” he said.

Colorado Parks and Wildlife placed four cages containing fish in the Animas River to monitor what happens to them, said spokesman Joe Lewandowski. The cages were placed at 32nd Street, the fish hatchery, Dallabetta Park and the High Bridge.

“We’ll see if those fish survive,” Lewandowski said. “We’re also monitoring to make sure we don’t get infiltration into the hatchery, because that could be a problem.”

Local officials have asked all agricultural water users to shut off water intakes.

Durango resident Lisa Shaefer said she was near the mine at Gladstone on Wednesday when a mine bulwark seemingly broke and sent a torrent of water downstream that raised the water level 2 to 3 feet in Cement Creek. The initial wall of water carried rocks and debris and made a roar as it pushed through a culvert, she said.

“What came down was the filthiest yellow mustard water you’ve ever seen,” she said.

In a statement, Nancy Agro, an attorney for San Juan Corps, which owns Gold King, placed the blame for the accident on the EPA: “The U.S. Environmental Protection Agency, operating under an access agreement obtained from the owner of the Gold King Mine, had begun an investigation regarding the source of contaminated water at the Gold King Mine last year. Upon suspending work last year, the USEPA backfilled the portal to the mine. On August 5th, 2015, while the USEPA 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 into the Animas River.”

For decades, the pollution flowing out of Silverton’s mines and into regional waterways has been so bad, the EPA has repeatedly threatened to list parts of the basin a Superfund site.

Peter Butler, co-coordinator of the Animas River Stakeholders Group and former chairman of the Colorado Water Quality Control Commission, said everyone invested in improving the Animas River’s water quality wanted to get into Gold King because for years, it has been one of the two biggest contributors of toxic water to the heavy metal loads in the Animas Basin.

“They had a plan for handling the mine pool but something went wrong and it all came blowing out,” Butler said.

Before the breach, Butler said the water being discharged from Gold King carried high concentrations of iron, aluminum, cadmium, zinc and copper.

While he didn’t know precisely the metal levels in the water that surged out of Gold King on Wednesday, Butler said: “I’m sure they were really high.”

Though Gold King has no record of emitting mercury, Butler said “when old mines open up like that, mercury sometimes drains out. Possibly, some other metals might have been released, like lead and arsenic. But there’s no evidence of that at this point.”

The contaminated water made its way to Bakers Bridge in La Plata County as of Thursday morning and hit town by Thursday evening. The material was expected cross the New Mexico state line between 4 and 5 a.m. Friday and arrive in Farmington on Friday evening.

Butler said Colorado Division of Reclamation, Mining and Safety scientist Kirstin Brown had tested pH levels – the telltale measure of acidity in water – in the Animas River at Trimble Lane when the toxic plume arrived.

The pH level dropped from 7.8 to 5.8.

“That’s a pretty big drop,” Butler said.

Farmington city officials shut down all water-supply intake pumps to avoid contamination and advised citizens to stay out of the river until the discoloration has passed.

The discharge consists of water that was being held behind unconsolidated debris near an abandoned mine portal.

Several mine workers were at the site at the time of the breach; all were unharmed, according to the EPA.

Silverton does not use water from Cement Creek, so its water source remained uncontaminated, said William Tookey, the San Juan county administrator who met with EPA officials on Thursday.

The Animas River was looking healthier about 24 hours after the discharge in Silverton, he said.

This is not the first time there has been a water-related accident at one of the mines, but it did come as a surprise to the town, Tookey said.

He was not sure if the release would change attitudes toward the EPA in town. For years, some town residents and local officials have been opposed to a Superfund listing.

“Since it was the EPA that was responsible for this, it may make people less likely to be open to them,” he said.

Colorado Department of Public Health and the Environment notified water users downstream of the release so they can take appropriate steps to turn off intakes until the contaminated water passed.

The EPA downplayed the potential effects on aquatic life, saying there is long-standing water-quality impairment issues associated with heavy metals in Cement Creek and upper portions of the Animas River. As a result, there are no fish populations in the Cement Creek watershed, and fish populations have historically been impaired for several miles downstream of Silverton in the Animas River, the release said.

Butler said it remains to be seen whether the toxic metal concentrations flowing downriver will impact the few fish species living below Bakers Bridge. But if the plume does have a negative impact on aquatic life, Butler estimated that fish would die within hours of contact with the plume.

EPA teams will be sampling and investigating downstream locations over the next several days to confirm the release has passed and poses no additional concerns for aquatic life or water users.

“This unfortunate incident underscores the very reason EPA and the state of Colorado are focused on addressing the environmental risks at abandoned mine sites,” said David Ostrander, director of EPA’s emergency response program in Denver. “We are thankful that the personnel working on this mine cleanup project were unharmed. EPA will be assessing downstream conditions to ensure any impacts and concerns are addressed, as necessary.”