Saint Lawrence Seaway (Iroquois Canal to Lake Ontario)

The exact dimensions of the largest boat that can travel on the waterway are not known. The maximum headroom is not known. The maximum draught is not known.
Iroquois Canal (southern entrance) | |||
Ogdensburg-Prescott International Bridge | 10.06 miles | 0 locks | |
Thousand Islands Bridge | 52.59 miles | 0 locks | |
Lake Ontario (northeastern entrance) | 79 miles | 0 locks |
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Wikipedia has a page about Saint Lawrence Seaway
The Saint Lawrence Seaway (French: la Voie Maritime du Saint-Laurent) is a system of locks, canals, and channels in Canada and the United States that permits oceangoing vessels to travel from the Atlantic Ocean to the Great Lakes of North America, as far inland as Duluth, Minnesota, at the western end of Lake Superior. The seaway is named for the Saint Lawrence River, which flows from Lake Ontario to the Atlantic Ocean. Legally, the seaway extends from Montreal, Quebec, to Lake Erie, and includes the Welland Canal.
The Saint Lawrence River portion of the seaway is not a continuous canal; rather, it consists of several stretches of navigable channels within the river, a number of locks, and canals along the banks of the Saint Lawrence River to bypass several rapids and dams. A number of the locks are managed by the St. Lawrence Seaway Management Corporation in Canada, and others in the United States by the Saint Lawrence Seaway Development Corporation; the two bodies together advertise the seaway as part of "Highway H2O". The section of the river from Montreal to the Atlantic is under Canadian jurisdiction, regulated by the offices of Transport Canada in the Port of Quebec.