They caused the accident by breaching a tailings dam while attempting to drain ponded water near the entrance of the mine on August 5.

[3] After the spill, the Silverton Board of Trustees and the San Juan County Commission approved a joint resolution seeking Superfund money.

[4] Contractors accidentally destroyed the plug holding water trapped inside the mine, which caused an overflow of the pond, spilling three million US gallons (eleven thousand cubic metres) of mine waste water and tailings, including heavy metals such as cadmium and lead, and other toxic elements, such as arsenic,[5] beryllium,[5] zinc,[5] iron[5] and copper[5] into Cement Creek, a tributary of the Animas River and part of the San Juan River and Colorado River watershed.

"[7] The EPA has taken responsibility for the incident, but refused to pay for any damages claims filed after the accident on grounds of sovereign immunity, pending special authorization from Congress or re-filing of lawsuits in federal court.

The spill affected waterways of municipalities in the states of Colorado, New Mexico, and Utah, as well as the Navajo Nation.

[15] Locals had feared that classifying this as a Superfund site would reduce tourism in the area, which was the largest remaining source of income for the region since the closure of the metal mines.

[19] In the absence of drainage, by 2002 a new discharge of particularly contaminated water had begun to flow from the Gold King Level 7 adit.

[20]: A-4 The impact on the Animas River was quickly visible; one Durango-based journalist described the water color after the accident as "Tang that has been maybe mixed too thickly.

[24][note 2] People living along the Animas and San Juan rivers were advised to have their water tested before using it for cooking, drinking, or bathing.

By August 10, the waste had reached the San Juan River in New Mexico and Shiprock (part of the Navajo Nation), with no evidence to that date of human injury or wildlife die-off.

[9] On August 12, the leading edge of the plume was no longer visible due to dilution and sediment levels in the river.

[33] On August 10, 2015, the EPA reported that levels of six metals were above limits allowed for domestic water by the Colorado Department of Public Health and Environment.

[36] EPA authorities had learned of this risk through a June 2014 work order that read "Conditions may exist that could result in a blowout of the blockages and cause a release of large volumes of contaminated mine waters and sediment from inside the mine, which contain concentrated heavy metals."

[36] On February 11, 2016, the Denver Post reported that Hays Griswold, the EPA employee in charge of the Gold King mine, wrote in an e-mail to other EPA officials "that he personally knew the blockage 'could be holding back a lot of water and I believe the others in the group knew as well.

"[39] On August 8, Colorado Governor John Hickenlooper declared a disaster,[5] as did Navajo President Russell Begaye.

[40] On August 11, New Mexico Governor Susana Martinez also declared a state of emergency, after having viewed the affected river from a helicopter, and said her administration was ready to seek legal action against the EPA.

[43] Following the spill, the local governments of Silverton and San Juan County decided to accept Superfund money to fully remediate the mine.

[4] The Federal Emergency Management Agency (FEMA) rejected a request by the Navajo Nation to appoint a disaster-recovery coordinator.

[44] In June 2018, the EPA proposed a $10 million interim clean-up plan that was met with criticism for showing no actual benefit.

Peter Butler of the Animas River Stakeholders Group wrote, "why is EPA not prioritizing where it can get the 'biggest bang for the buck' in terms of dollars spent for mine remediation?"

[45] In April 2018, the Associated Press reported on allegations from the Sunnyside gold corp. which claim the EPA was "running its treatment plant at a fraction of capacity" and that "more than 350 million gallons (1.3 billion liters)—150 times the volume of the Gold King spill—have flowed around the treatment plant into a tributary of the Animas" since October 2015.

[52] The truck was hauling the waste to a new storage facility by Silverton, after a similar plant in Durango ran out of room.

[53] The effects of the Gold King Mine spill on the Navajo Nation has included damage to their crops, home gardens, and cattle herds.

While San Juan County in New Mexico lifted the ban on water from the San Juan River on August 15, 2015, the President of the Navajo Nation, Russell Begaye, who had ongoing concerns about the water's safety, did not lift the Navajo Nation's ban until August 21, 2015.

As of April 22, 2016, the Navajo Nation has been compensated a total of $150,000 by the EPA, according to testimony at hearings of the Senate Committee on Indian Affairs.

[56] The EPA is now motioning to dismiss all lawsuits, stating that they have paid enough through the $29 million they have spent to clean up the Animas River and other contaminated areas.