Whonnock Lake is not as Wikipedia says, a man-made lake.
It is a natural muskeg lake and, if left alone, it will slowly turn into a peat marsh.The only regular water input is from the north. There is an exit to Whonnock Creek on the south-east side originally closed off by a sandbar (beaver dam) that was replaced in 2008 by a man-made berm and fish channel. This is where the water escapes from the lake to Whonnock Creek.
In the past beavers regulated the water level of the lake — now the city does that.