See also: Fifth (homonymy)

The bay of Fifth (English: Bay off Fifth) is located at the Canada in the province of the Ontario on northern bank of the Lake Ontario to approximately 200 km in the east of the town of Toronto and to 400 km in the west of the town of Montreal. The bay which is narrow with the form of a Z . It naturally separates the peninsula from Prince Edouard of the remainder of the province. Its width exceeds only very seldom 2 km whereas its length reaches more than 100 km. The bay stops on the level of the town of Trenton close to the mouth of the Rivière the Trent which belongs to the inland waterway the Trent-Severn connecting the Lake Ontario to the Lake Huron on the level of the Baie Georgienne.

The bay had a big role during the period of the Prohibition to the the United States. The alcohol manufactured in the area was sent by boats through bay and the Lake Ontario to the United States. This illegal trade was at the base of the creation of many fortunes in the area of the city of Belleville.