Spongy Lake (near Waterloo, Ontario), back in 1983 when I thought those glasses were a good idea and geographers had to have mustaches. This is a kettle lake, which started off as a chunk of ice broken off from retreating glacial ice.
Over the years the ice melted, leaving a deep, cold lake inside a crater. It also has one of the few peat bogs in southern Ontario and is very important to local groundwater hydrology. It was an important and enjoyable field research area when I was studying physical geography at the University of Waterloo.