Minnesota Public Radio: When the American Century cargo ship glides beneath the Aerial Lift Bridge into Duluth, dock workers will spring to action, ready to load it with coal.
But when the 1,000-foot "laker" departs, its holds won't be full. Before workers can fully load the ship, it must first clear a shallow spot in the St. Mary's River after passing through the Soo Locks. The river connects Lake Superior to Lake Huron, which is at record low levels.
"They have to make sure they have enough under-keel clearance...