From 1952 to 1978, Anaconda Copper Company operated the open-pit Yerington Copper Mine. During that time, the mine produced approximately 165 million tons of copper. Anaconda got out of the copper-mining business, it was rumored, in part to avoid tightening environmental regulations, although falling copper prices were certainly a factor. Later, there was some small-scale mining involving reprocessing stockpiled ore and spoil with newer technology, but all that activity is also now defunct.
Once the mine stopped operating and pumping ceased, the open pit began filling with water as a result of groundwater seepage. Now the former mine has turned into a roughly rectangular lake that measures about a mile long and 1,600 feet wide. As of 2020, the water was about 500 feet deep and still filling at the rate of some 10 acre-feet (about 3.3 million gallons) per year. The increase will cease when the level becomes even with the water table.
Unsurprisingly, the U.S. Environmental Protection Agency has designated the area a Superfund site. At present, often-acrimonious discussions continue with regards to what remediation efforts should be undertaken and who will pay for them.