Underground lake - online puzzles

An underground lake or subterranean lake is a lake under the surface of the Earth. Such lakes may be associated with caves, aquifers, or springs. They are typically very low in salinity.

The largest non-subglacial lake in the world is in Dragon 's Breath Cave in Namibia, with an area of almost 2 hectares (5 acres), and the second largest is in Craighead Caverns in Tennessee, United States.