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Most natural lakes in North America were formed by glaciers, though Maryland, for example, is notably missing natural lakes because it was never glaciated.

Deep lakes often form a three-layered structure in summer: a warm upper layer ( epilimnion ), a middle transition layer ( metalimnion ), and a cold bottom layer ( hypolimnion ). Most natural lakes in North America were formed

The open water area away from the shore, which is well-lit (photic zone) and dominated by plankton. Most natural lakes in North America were formed