After the Ice Age, around -13 000 years, Montreal and the Saint Lawrence Lowlands are flooded by the Champlain sea. Within a few centuries, as and when these waters recede, the Mount Royal and its three summits are emerged into islands. With the complete withdrawal of the sea, water is retained in some depression of the island. This is the case among other Beaver Lake, located in the palm of Mount Royal. This will dry gradually to become a fen. He was regrooved artificially in 1938.