The accidental breaching of a dam at a long-closed gold mine in Colorado could adversely impact Lake Powell at Glen Canyon National Recreation Area in Utah this week.

Park officials say wastewater carrying heavy metals released from the mine on the Animas River in Colorado is expected to arrive at Lake Powell via the San Juan River early this week. The accidental release occurred as crews from the Environmental Protection Agency and contractors were trying to drain water from behind the dam and caused a failure in the dam.

While contaminant levels and impacts anticipated at Lake Powell are not yet understood, as a precautionary measure the National Park Service at Glen Canyon National Recreation Area is encouraging visitors to avoid drinking, swimming, or recreating on the San Juan River within Glen Canyon National Recreation Area and on the San Juan River arm of Lake Powell until further notice.

Most river sediments will settle out of the water when the river current slows at Lake Powell, as is illustrated by the sediment deltas at the mouths of all rivers entering the lake. Even if all of the contaminants do not settle out of the water at the San Juan River sediment delta, because of the extremely slow rate of movement down the 40-mile San Juan River arm of Lake Powell, at this time the alert is not being issued for the entire lake.

Some impacts to natural resources in the San Juan River and the lake are anticipated as contaminants settle into the sediment. Impacts will be monitored by the park. Those planning to recreate in the area should monitor the situation as more information becomes available.