Lava lake

Lakes are small, widespread, naturally-generating structures which contain volumes of different fluids.

Ice paths are highly lake-like structures which resemble frozen lakes.

Description
Lakes are shallow and often small bodies of liquid. Water lakes, which are small pools of water springs, can generate above sea level or inside caverns. They can also generate isolated underground, connected to no other structures whatsoever. When in a winter biome, these small lakes are never initially frozen but turn to ice if exposed. The lakes can also be composed of lava; however, lakes of lava are much rarer. Lava lakes found at the surface are surrounded by stone (which can be replaced by ore veins such as dirt, gravel and coal). Both types of lake generate with a small air pocket above them, which may result in floating sand, floating snow cover or even the top two-thirds of trees above the lake. Lava lakes may cause trees to burn away.

Generation
Lakes generate basically anywhere. Water lakes generate the most commonly, and in almost all overworld biomes, excluding some desert variants. Lava lakes are considerably rarer, and generate stone around them replacing blocks. Ice paths generate exclusively in the Ice Spikes biome.

Lakes which attempt to spawn in midair are instead lowered down to the highest solid terrain below them. Superflat worlds with them enabled will have way more lakes if the top is at a lower level than worlds which are tall.