Welland Canal Port Maitland. With the opening of the extension, the canal stretched between the two lakes, with 40 wooden locks. The minimum lock size was , with a minimum canal depth of . Deterioration of the wood used in the 40 locks and the increasing size of ships led to demand for the Second Welland Canal, which used cut stone locks, within just a few years. In 1839 the government of Upper Canada approved the purchase of shares in the private canal company in response to the company's continuing financial problems in the face of the continental financial panic of 1837.
Welland Canal updated systems for Locks 1 through 7 will be completed in 2017. In the 1950s, with the building of the present St. Lawrence Seaway, a standard depth of was adopted. The long Welland By-Pass, built between 1967 and 1972, opened for the 1973 shipping season, providing a new and shorter alignment between Port Robinson and Port Colborne and by-passing downtown Welland. All three crossings of the new alignment—one an aqueduct for the Welland River—were built as tunnels. Around the same time, the Thorold Tunnel was built at Thorold and several bridges were removed. These projects were to be tied into