A glacial lake is a lake with origins in a melted glacier.

Glacial lakes can be green in colour. This is the result of ground up minerals (rock flour) being consumed by algae. Nova, Mystery of the Megaflood, ^*, PBS

A retreating glacier often leaves sections of ice behind, in hollows between drumlins or hills. As the ice age ends these will melt to create lakes. These lakes are often found surrounded by drumlins, along with other evidence of the glacier, such as moraines, eskers and erosional features such striations and chatter marks.

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