BILLINGS, Mont. (AP) — A once-contaminated creek flowing into Yellowstone National Park may be clean enough to be removed from the impaired waters list.

The Montana Department of Environmental Quality is close to removing 5 miles of lower Soda Butte Creek from the list.

Prior to the cleanup effort, which was completed in 2014, the creek was contaminated by toxic runoff from copper, gold and silver extraction from an old mining district.

The stream was so toxic that no fish could live in that stretch of water.

The creek now meets Montana's water quality standards for heavy metals. Copper and lead levels still remain unresolved in sediments. Further analysis of what's causing the contamination will continue.