Editor’s note: This is the first of two parts. Click here to read Part 2.

On Aug. 5, about 3 million gallons of contaminated water burst out of an abandoned mine above Silverton and sent a plume of cloudy, orange water down Cement Creek to the Animas River, through the heart of Durango, and on into the San Juan River in New Mexico, the Navajo Nation and Utah. Downstream: Lake Powell.

The plume of acidic orange water, containing arsenic, lead and other toxic heavy metals, had built up as a result of historic mining activity dating back to the 1870s, as well as work to plug some mines, which ultimately redirected contaminated water into others. The massive plume was set loose by workers for the U.S. Environmental Protection Agency attempting to assess and remediate the source of an ongoing trickle of pollution from the Gold King mine.

Small Impact

Fortunately, immediate biological impacts appear to be less dramatic than the appearance of the water suggests. Colorado Parks and Wildlife has been holding fish in cages in the Animas River to see if exposure to the plume would kill them, and so far it hasn’t. The Mountain Studies Institute reports that the small bugs that live in the stream bed and make up the base of the aquatic food chain also seem to be holding on at their sampling sites in the Durango area. The fact that the highest concentrations of contaminants passed through the area fairly quickly seems to have helped.

In terms of human health impacts, drinking water intakes on the Animas River for Durango; Farmington, New Mexico; and other communities were shut off before the plume arrived. These communities are relying on stored water and other sources for the time being.

Medium term, irrigators relying on the Animas and San Juan rivers could lose crops if they don’t get the go-ahead to open up their diversions again soon and/or get lucky with rain. And rafting companies are certainly feeling an economic hit as people are kept off the river.

Exposure to Contaminants

Longer term impacts are harder to assess, since health impacts to both people and wildlife depend on the level and duration of exposure to the contaminants. It’s clear that the heavy metals will settle out into the sediments on streambeds and the bottom of Lake Powell, but it’s not clear how concentrated the contaminants will be and to what extent they will move back into the water column in response to storms and floods.

Overall Regional Water Picture

In assessing how this catastrophe fits into the overall regional water picture, it is instructive to zoom out geographically and look back in time. The 3 million gallons of contaminated water from the spill translate to a little over 9 acre-feet of water. This quantity is dwarfed by the approximately 13 million acre-feet currently in Lake Powell, despite the fact that it is only 54 percent full. Particularly given that the heavy metals will increasingly drop into the lake floor as the water slows down, impacts to the Grand Canyon and downstream water users should be minimal.

Looking back in time, Jonathan Thompson points out in a web article for High Country News called “When our river turned orange,” that pollution of the Animas River from mines has been a problem for over 100 years, with previous dramatic blow-outs, and waxing and waning impacts to fish as remediation efforts have gained and lost ground.

Looking ahead, this latest catastrophe may stimulate more comprehensive solutions to this longstanding problem, in the Animas Watershed and around the region. Check out Part 2 to learn more about how the spill on the Animas relates to the Eagle Valley.

Hannah Holm is coordinator for the Water Center at Colorado Mesa University. Holm is a friend of the Eagle River Watershed Council, which has a mission to advocate for the health and conservation of the Upper Colorado and Eagle River basins through research, education and projects.

This article ran in the Vail Daily on August 22, 2015.