Short answers, pulled from the story.
A lake is a naturally occurring, relatively large and fixed body of water localized in a basin surrounded by dry land. Lakes lie completely on land and are separate from the ocean, though rivers may connect them. There is no internationally accepted scientific definition distinguishing a lake from a pond.
Lakes cover approximately 2.5 million square kilometers of the Earth's surface, which is less than 2 percent. Most lakes are fresh water and account for almost all of the world's surface freshwater, although some salt lakes are saltier than seawater.
In 1957, G. Evelyn Hutchinson classified lakes by origin into 11 major types divided into 76 subtypes. The 11 types are tectonic, volcanic, glacial, fluvial, solution, landslide, aeolian, shoreline, organic, anthropogenic, and meteorite lakes. Glacial lakes are the most numerous in the world.
Lake Baikal in Siberia is the deepest lake in the world, with a bottom at 1,637 meters and a mean depth of 749 meters, the greatest in the world. It is also the oldest lake and the largest freshwater lake by volume at 23,600 cubic kilometers.
The Caspian Sea is the largest lake by surface area at 371,000 square kilometers, considered a lake in geography despite its name. The largest freshwater lake by surface area is Lake Michigan-Huron at 117,400 square kilometers, which is hydrologically a single lake.
Lakes slowly fill with sediment and become wetlands such as swamps or marshes, and reeds accelerate this by decaying into peat. Thawing permafrost may explain the shrinking of hundreds of large Arctic lakes in western Siberia. Between 1990 and 2020, more than half of the world's large lakes decreased in size, partly due to climate change.