The Welland Canal is a ship canal that runs 43.4 km from Port Colborne, Ontario on Lake Erie to Port Weller, Ontario on Lake Ontario. It allows ships to avoid Niagara Falls by traversing the Niagara Escarpment. About 40 million tonnes of cargo passes through the canal annually. It also provides water for industry and a small amount of electricity.

The Port Weller end of the canal is 99.5 m lower than the Port Colborne end. There are eight locks, each 24 m by 234 m. The canal is 9 m deep.

The current canal, the fourth, was built between 1913 and 1932. Between the years of 1967 and 1973 a channel was constructed east of the city of Welland, Ontario to help speed ship traffic through the canal and alleviate highway traffic through the rose city. This channel is known as the Welland By-Pass. The first canal, built by William Merritt , was completed in 1833. It was something of a debacle. The poor construction caused problems and it was never profitable. It was eventually bought out by the government of Upper Canada. Along with those of the Cornwall Canal its losses caused the bankruptcy of the Upper Canada government contributing to the 1840 Act of Union.

The canal, part of the St Lawrence Seaway, was named after the Welland River.