Clarence St. Bridge, Vertical-lift bridge in Port Colborne, Canada.

The Clarence Street Bridge, also called Bridge 21, is a vertical-lift bridge over the Welland Canal in Port Colborne, Ontario. Electric motors and counterweights raise its deck 36.5 metres above passing vessels, a lift or lowering that takes about 90 seconds. Its western approach crosses former canal locks 26 and 27, which the approach made inoperable.

This bridge was built between 1927 and 1929 as part of the canal's expansion and modernization. It replaced older crossing structures to handle the growing ship traffic through the waterway.

The bridge carries Clarence Street across the canal and is known locally as Bridge 21, the number it holds among the Welland Canal's crossings. Its deck rises about 36.5 metres above passing vessels, and the lift takes roughly 90 seconds, so pedestrians on the approach can watch a laker or freighter pass beneath.

The lifting mechanism operates smoothly to let ships through, and visitors can watch the process from the bank or walk across when it is lowered. The bridge is accessible year-round and offers views of the waterway and surrounding area.

Bridge 20, a second vertical-lift span built in 1927–1929 by the Canadian National Railway, stood just north of Bridge 21. The completion of the Port Colborne Harbour Railway in the mid-1990s linked the city to rail lines west of the canal, making it redundant; it was removed in the winter of 1997.