<P> The majority of lakes on Earth are fresh water, and most lie in the Northern Hemisphere at higher latitudes . Canada, with a deranged drainage system has an estimated 31,752 lakes larger than 3 square kilometres (1.2 sq mi) and an unknown total number of lakes, but is estimated to be at least 2 million . Finland has 187,888 lakes 500 square metres (5,400 sq ft) or larger, of which 56,000 are large (10,000 square metres (110,000 sq ft) or larger). </P> <P> Most lakes have at least one natural outflow in the form of a river or stream, which maintain a lake's average level by allowing the drainage of excess water . Some lakes do not have a natural outflow and lose water solely by evaporation or underground seepage or both . They are termed endorheic lakes . </P> <P> Many lakes are artificial and are constructed for hydro - electric power generation, aesthetic purposes, recreational purposes, industrial use, agricultural use or domestic water supply . </P> <P> Evidence of extraterrestrial lakes exists; "definitive evidence of lakes filled with methane" was announced by NASA as returned by the Cassini Probe observing the moon Titan, which orbits the planet Saturn . </P>

Where does the water in a lake come from