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The construction project involved not just construction, dredging, power plant construction, dam building, and lock development, but also the relocation of scores of people who resided along the banks of the proposed Seaway.  Before construction could commence, the displaced persons had to be compensated for their properties and relocated. On the American side, things weren't too difficult since the area was sparsely populated, but the Canadian side required the movement of more than 6,500 people to new towns built by the project.

After all affected people were relocated, construction began in earnest. The impressive task required:

• removal of 192.5 million cubic meters of earth
• pouring of more than 5.7 million cubic meters of concrete
• building 72 kilometers of dikes
• digging 110 kilometers of channels
• increasing the 14-foot depth to 27 feet
• removing 30 existing locks
• enlarging existing canals (i.e. Beauharnois Canal and Welland Canal)
• installing 15 new locks each having 766 feet of usable length, 80 feet of usable width, and 30 feet of depth
• construction of spillway dams (i.e. Long Sault Dam)
• construction of control dams (i.e. Iroquois Dam)
• construction of power generation dams (i.e. Saunders-Moses Dam)
  

After just five years, the St. Lawrence Seaway was officially opened on April 25th, 1959, and linked the Atlantic Ocean to the Great Lakes. The official opening ceremonies were held three months later on June 26, 1959, in the presence of Queen Elizabeth II (representing Canada) and President Dwight D. Eisenhower (representing the United States).

Overall, the project cost $470 million US dollars, of which $336.2 million were paid by Canada and $133.8 million were paid by the United States. Income from the operating the Seaway is shared proportionately.