TVA released black muck from the Copper Basin Dam in east Tennessee last week while trying to repair a series of dams on the Ocoee River—a prized whitewater river and site of the canoe and kayak events for the 1996 Olympic Games.

According to the Tennessean, TVA did not contact any state or federal agencies about the spill, nor did they get permits to repair the dam. U.S. Forest Service officials discovered the spill this past Sunday. Dead fish lined the river, and countless others had already been washed down stream in the thick mire coating the river. The mucky sediment released by the ruptured dam contained toxic chemicals from mining operations in the region.

Copper mining nearly wiped out the Ocoee’s aquatic life in the early 1900s, but a century of conservation and cleanup had helped restore the Ocoee to a relatively healthy waterway. Last week’s spill will likely wipe out decades of conservation efforts.

The Ocoee is one of the most popular whitewater rivers in the country. Kayakers, canoeists, and commerical rafting companies flock to the Ocoee for its non-stop, class II-IV rapids.