Lake Manly was a large freshwater lake which filled the Death Valley (United States) basin prior to the dry climatic period which has prevailed since the last ice age. Lake Manly receded due to increased evaporation, and to isolation from the Colorado River system, to which it was once connected.

As Lake Manly evaporated to the surface of Death Valley, it left a remarkable legacy. Under the surface of Death Valley is one of the world's largest underground reservoirs (aquifers). Being fed by the Amargosa River and Salt Creek , this aquifer is barely visible above ground at Badwater, California. Badwater, the lowest point in the valley (282 feet below sea level), is just low enough to reveal groundwater.

Shoreline Butte has easy to see weak shorelines on it called strandlines that were formed by wave action from Lake Manly. These features were created by different stands of the lake, which would change its depth over time and slight changes in climate. The conditions under which this lake existed are called 'pluvial ' by geologists instead of glacial because glaciers did not directly touch Death Valley - but the meltwater from the glaciers and the cooler and wetter temperatures of the time did affect the valley. There is something like 8000 feet (about 2500 m) of gravel, sand, and mud overlying the bedrock of the valley floor.

In 2005, large amounts of flooding resulted in Lake Manly appearing on a large scale. Over a hundred square miles were covered by the lake and a couple park rangers became probably the only humans to canoe across the valley. The lake was about two feet at its deepest point. As a result, it evaporated quickly, leaving behind a mud-salt mixture.