St. Peters Canal

The St. Peters Canal is a small shipping canal located in eastern Canada on Cape Breton Island. It crosses an isthmus in the village of St. Peter's, Nova Scotia which connects St. Peters Inlet of Bras d'Or Lake to the north with St. Peters Bay of the Atlantic Ocean to the south.

A "haulover road" across the isthmus established by French fur trader Nicholas Denys in 1650 predated the canal. A feasibility study was conducted in 1825 into the possibility of building a canal. Construction began in 1854 and was completed in 1869, resulting in a channel measuring 800 m (2,600 ft) long and an average of 30 m (100 ft) wide. The canal passes through a 20 m (65 ft) high hill composed of solid granite, accounting for the 15 years for its construction. There can be a tidal difference of up to 1.4 m (4.5 ft) between Bras d'Or Lake and the Atlantic Ocean, thus a lock was designed to regulate water levels.

The St. Peters Canal saw relatively heavy use by commercial shipping in the 19th century and early 20th century, during an era of industrial expansion on Cape Breton Island. The canal soon became too small for modern ships and has been used primarily by pleasure boats since the end of the Second World War. The canal was designated a National Historic Site of Canada in 1925 and is now operated and maintained by Parks Canada.

Parks Canada undertook a major project to restore both entrances to the canal in 1985. The St. Peters Canal is operational from May to October each year. Vessels transiting the canal are limited by the size of the lock, which measures 91.44 m (301 ft) long, 14.45 m (47 ft) wide, and 4.88 m (16 ft) draught.

In the vast majority of canals the flow of water is unidirectional. That is, the "high" side of the canal is always the same. St. Peter's Canal is unusual in that, due to the difference in the timing of the tides between Bras d'Or Lake and the ocean, sometimes it's the Atlantic side that is the higher, sometimes it's the lake side. As a result, the canal requires special "double" gates, the only ones of their kind in North America. The usual canal lock has a gate at each end, each gate consisting of two swinging doors that when closed form a shallow 'V' shape, with the point of the 'V' pointing upstream. At the St. Peter's Canal lock each gate consists of four swinging doors which form a diamond shape when closed. In actual use the pair of doors which form the upstream pointing 'V' are used. No matter which side has the higher water level, either one pair or the other will be appropriate.