Since 2002 it has been subject to dry-season level drops of as much as . The last such level fluctuations occurred between 1751 and 1804 as historical accounts give widely different accounts of the lake size. From 2008 to 2020, Mountain Lake was nothing more than a reddish-brown pit, only partially filled with water. The lake's water levels had fluctuated dramatically over the previous 20 years. It first dropped in 1999, and returned to its normal levels in 2003. In 2006, it dropped again, and emptied completely for several days, leaving behind dead and rotting fish. From 2008 to 2012, it was mostly empty. However, resort employees noticed that the lake had begun to refill during a wet spring of 2020, and the lake had refilled to about a third full by July 14th. During the lake's most recent dry period, researchers had examined the area's geology and concluded that the lake existed on a natural rise-and-fall cycle. During dry periods, accumulated sediment is believed to move through a natural plumbing system consisting of the aforementioned openings in the lake bottom. The lake is now believed to reach its lowest points on a roughly 400-year cycle.