A toxic leak of wastewater that has turned a Colorado river mustard yellow is three times larger than US officials had originally estimated.
The Environmental Protection Agency (EPA) now says that 3 million gallons of wastewater spilled from an abandoned mine last week.
The EPA does not believe wildlife is in significant danger because the sludge moved so quickly downstream.
Local authorities took steps to protect drinking water supplies and farms.
The spill began on 5 August when EPA workers, who were cleaning up the closed Gold King Mine, accidentally sent the toxic water flowing into a tributary of the Animas River.
The Animas River has been closed and local officials have advised people to stay out of the water.
The EPA is meeting with Colorado residents this week and testing local wells for contamination. More than 1,000 wells may have been contaminated.
"We're going to continue to work until this is cleaned up and hold ourselves to the same standards that we would anyone that would have created this situation." Shaun McGrath, an EPA official, told residents at one of the community meetings, according the New York Times.
Some residents derided the agency, calling it the "Environmental Pollution Agency".
The EPA is still investigating the health effects of the leak, which included heavy metals including lead and arsenic.
The discoloured water, which is now beginning to dissipate, stretched more than 100 miles into neighbouring New Mexico.