Most lakes in Frontenac were formed during the ice age by glaciers which scraped the earth down and formed deep basins which later filled with water. This happened thousands of years ago, but if you went back a few hundred years Bobs Lake would be virtually unrecognisable.

Originally, in the place where Bobs Lake is now, there was a river valley with four smaller lakes. The lands were inhabited by the Mississauga in the 1700s. They were later settled by Nipissing and Algonquin peoples, as well as European immigrants in the early-to-mid-1800s.

It was around this time that Canada and the United States signed the treaty of Ghent, ending the War of 1812. Tensions were still high following the war, and as a precautionary measure Canada built the Rideau Canal: a waterway from Ottawa to Kingston that passes alongside Frontenac. It was this waterway that eventually led to the formation of Bobs Lake.

In the 1860s, after years of drought, the river valley was flooded in order to provide a larger reservoir of water for the Rideau Canal. Initially, the water level was only supposed to rise by two feet, so it took the community and government officials off guard when the water levels rose by over 15 feet. Forest, roads, and bridges were destroyed, and Bobs Lake was born.

Today Bobs Lake has a distinctly firm shore due to the flooding, and the remains of some of the flooded trees can still be seen. Crow Lake remained unchanged over this period, but since the new Bobs Lake was at a similar elevation, eventually the two were joined by a channel for navigation.