Taum Sauk Hydroelectric Power Station, Pumped-storage power station in Reynolds County, Missouri.

Taum Sauk Hydroelectric Power Station sits on Proffit Mountain in Reynolds County, Missouri, about 90 miles south of St. Louis. Its upper reservoir is a flat basin enclosed by a dam nearly 100 feet tall, lined with pale gray concrete panels and a dark blue-black strip along the lower edge; a yellow crane stands on the drained floor. A 7,000-foot tunnel through the mountain connects it to the 450 MW plant below.

The facility started operating in 1963 and supplied the surrounding region with hydroelectric power. Following a major dam failure of the upper reservoir in 2005, the entire station was completely rebuilt and modernized.

The plant's operator calls Taum Sauk "the biggest battery that we have", because it stores energy rather than generating it from a natural inflow. Its pump-turbines were the largest ever built when the station opened, and it was the first pure pumped-storage plant in the United States.

The site operates to supply power during peak demand times and stores water at night when electricity use drops. Visitors should know this is an active industrial facility and public access may be limited.

The rebuilt upper dam, completed in 2010, is the largest roller-compacted concrete dam in North America, replacing the original rockfill embankment that failed in 2005. The reservoir it holds sits on the flat ridge of Proffit Mountain, not on Taum Sauk Mountain, about 5 miles to the east.