The Great Lakes constitutes the world's greatest collection of fresh water which amounts to one-fifth of the world's total surface supply. Four of the five lakes account for over half of the 2,342-mile (2,038nm) St. Lawrence Seaway's extension from the easternmost point on Lake Ontario to Duluth, Minnesota on the west. Maritime navigation has been extended through the Great Lakes with a minimum controlling depth of 27-feet throughout its length.
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