Many believe there are subterranean alien bases under lakes and oceans. UFO's are seen rising form the water by locals in places such as Lake Titicaca, where legends of ancient astronauts who visited the planet thousands of years ago, are common. USOs - Unidentified Submerged Objects -- In mythology, we often read about Amphibious Gods who rose from a body of water, sometimes a lake, and created humans.

Dogon Mythology - The Nommo

Geologic evidence appears to confirm, that ancient lakes once formed on the surface of Mars. It is also possible that volcanic activity on Mars will occasionally melt subsurface ice, creating large lakes. Under current conditions this water would quickly freeze and evaporate unless insulated in some manner, such as by a coating of volcanic ash.

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Saturn's largest moon, Titan. Photographs and spectroscopic analysis by the Cassini-Huygens spacecraft show liquid ethane on the surface, which is thought to be mixed with liquid methane.

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Jupiter's small moon Io is volcanically active due to tidal stresses, and as a result sulfur deposits have accumulated on the surface. Some photographs taken during the Galileo mission appear to show lakes of liquid sulfur on the surface.

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There are dark basaltic plains on the Moon, similar to lunar maria but smaller, that are called lacus (singular lacus, Latin for "lake") because they were thought by early astronomers to be lakes of water.