US states Colorado and New Mexico have declared emergencies after three million gallons of wastewater spilled into the Animas River from the Gold King Mine.
On 5 August, Environmental Protection Agency (EPA) workers accidentally triggered a breach at the mine in San Juan County during an investigation.
The investigation was aimed at evaluating the ongoing water releases from the site and to treat mine water, as well as assessing the feasibility of further mine remediation.
Loose material planned to be excavated collapsed into the cave entry.
The material pile then gave way, opening the adit and causing the spilling of water into Cement Creek that was stored behind the mound of materials.
The water discharge is estimated to have contained potentially harmful contaminants into Cement Creek, which flowed into the Animas River and continued downstream.
New Mexico Governor Susana Martinez said: "I had the chance to see the spill with my own eyes. It is absolutely devastating, and I am heartbroken by this environmental catastrophe.
"As I've said before, I am very concerned by EPA's lack of communication and inability to provide accurate information. One day, the spill is one million gallons. The next, it's three million."
EPA said it is monitoring water contaminated by the release by working with responders, as well as local and state officials.
High-concentrations of heavy metals such as arsenic, mercury and lead were found in the release and the discharge was continuing to flow at the rate of 500gal per minute.
Colorado Governor John Hickenlooper issued an executive order that allocates $500,000 to pay for the response and technical assessments, while New Mexico Governor Susana Martinez has declared $750,000 in state funds.
Hickenlooper said: "Our priority remains to ensure public safety and minimise environmental impacts.
"We will work closely with the EPA to continue to measure water quality as it returns to normal, but also to work together to assess other mines throughout the state to make sure this doesn't happen again."