After the Ice Age, around 13,000 years ago, Montreal and the Saint Lawrence Lowlands were flooded by the Champlain Sea.
Within a few centuries, as and when these waters receded, Mount Royal and its three summits emerged into islands.
With the complete withdrawal of the sea, water was retained in some depression of the island.
This was the case amongst others of Beaver Lake, located in the palm of Mount Royal.
Below is a partial list of current waters bodies of the island: