Georgian Bay, large northeastern extension of Lake Huron, S Ont., Canada, separated from Lake Huron by Manitoulin Island and by the Bruce Peninsula; Lucas Channel is its chief connection with Lake Huron. Rivers draining the lake regions of S Ontario flow into it; they include the French River, which, with North Channel, the northern connection of Georgian Bay with Lake Huron, forms part of the old voyageur's trading route from Montreal to the northwest. Georgian Bay is connected with Lake Ontario by the Severn River and Trent Canal. Christian Island is the largest in the bay. Many of the well-timbered, rock-bound islands of Georgian Bay are summer resorts. The Georgian Bay Islands National Park (5.4 sq mi/13.9 sq km; est. 1929) includes 40 of the islands and part of the mainland.