(Bloomberg) — An environmental cleanup of an abandoned mine in the mountains of Colorado went horribly wrong, leading to the spill of one million gallons of contaminated water into a creek that eventually drains into the San Juan River.

The incident happened when workers for the Environmental Protection Agency were trying to clean the long-abandoned Gold King Mine, but allowed it to breach a berm, or small strip of raised land, and the toxic water flowed into the Animas River. It turned the clear mountain stream a mustard orange color, according to photos posted online. The local sheriff's office on Aug. 6 closed the river to swimming, kayaking and rafting, and it remained closed Saturday.

"It's a sad irony that a program attempting to avoid harm to the environment, appears to have caused it," said Taylor McKinnon, public lands coordinator for the Center for Biological Diversity, a nonprofit group in Colorado. As the polluted waste moves downstream, "it will dilute, but we don't know what's in this water," McKinnon said.