A glacial lake is a lake with origins in a melted glacier. Glacial lakes can be green as a result of pulverized minerals (rock flour) that support a large population of algae. A retreating glacier often leaves behind large deposits of ice in hollows between drumlins or hills. As the ice age ends, these will melt to create lakes. These lakes are often surrounded by drumlins, along with other evidence of the glacier such as moraines, eskers and erosional features such as striations and chatter marks.