There's a lake that's actually a sinkhole - Apparently.
Lake Natron in Tanzania is a saline, alkaline lake that's a natural sinkhole, created by the evaporation of a volcanic spring. The lake's water is so alkaline that it can turn animals that die in it into statues, due to the high concentration of sodium carbonate. The lake's surface is also remarkably still, with no waves or ripples, due to the surrounding cliffs that block wind and waves. This phenomenon has been documented by scientists and is visible in satellite imagery.