The Big Rideau Lake is a lake situated in the province of Ontario (Eastern Ontario), Canada. The lake is located 72 kilometres (45 mi) to the southwest of Ottawa, Canada's capital city. It is 32 kilometres (20 mi) long and is 6 kilometres (3.7 mi) wide. The lake is much narrower at its northeastern end than at its southwestern end. The lake forms part of the Rideau Waterway, and is the largest lake along the route of the Rideau waterway. In 2007, the waterway was registered as a UNESCO world heritage site. The Upper Rideau Lake is connected to the Big Rideau Lake through the Narrows Lock at the southwestern end of the lake. The small community of Rideau Ferry is located at the junction between the Big Rideau and Lower Rideau Lake, at the northeastern end of the lake.