A bright-orange flow coming from the Golden Anchor mine and running into the Little Blackfoot River near Elliston is a confirmed blowout of the mine.

At this point, biologists are still learning whether fish were killed from the flow of water that's built up behind the abandoned mine's earthen plug at its adit, or entrance. When the water was sampled in the 1990s by the state, it contained arsenic, zinc, iron and other heavy metals, according to Lisa Peterson, a spokesperson for the Montana Department of Environmental Quality.

The mine is located on the Helena National Forest. It's number 68 on the state's Abandoned Mine Priority List for cleanups.

"The sampling done in the 1990s showed the water coming out of the adit did exceed water quality standards," Peterson said. "But at that point the flow was fairly minimally, which is why it's only listed as 68th.

"We obviously didn't foresee this happening."

Duane Harp, Helena district ranger, said the adit was plugged, probably when the mine was abandoned in the 1999s. As time passed, the mine started filling up with water for years.

"I don't really understand all the hydrology of it, but the water built up and blew the plug out," Harp said. "The water ran down the road and hit a tributary of the Little Blackfoot."

He said the pH of the water coming out of the mine shaft is a four, which is considered fairly acidic.

"But it's pretty murky, so we don't know about any fish kills just yet," Harp said.