The Soo Locks, Gateway Between Two Oceans of Fresh Water

At the city of Sault Sainte Marie, on the narrow river connecting Lake Superior to Lake Huron, the water drops twenty-one feet in less than a mile. The rapids there, Saint Marys Falls, the French called them, were a barrier that shaped the entire geography of the Great Lakes for centuries. Everything had to be portaged around them: canoes, furs, people, and eventually ore.

In eighteen fifty-three, the state of Michigan persuaded Congress to grant it land to finance a canal bypassing the falls. Two years later, on June eighteenth, eighteen fifty-five, the first ship passed through the completed Sault Sainte Marie Canal, the Soo Locks, as they came to be called. The engineer was a twenty-five-year-old named Harvey who had pushed workers through a brutal winter, but the canal they built that first season was only seventy feet wide.

Iron ore from the Marquette Range had been discovered the year before the canal opened. The timing was almost supernatural. The Soo Locks quickly became the single most critical shipping chokepoint in the American industrial economy.

Iron ore mined in the Upper Peninsula and, later, in Minnesota's Iron Range had to pass through Sault Sainte Marie to reach the steel mills of Chicago, Gary, Cleveland, and Pittsburgh. Coal moved northbound in return. In later decades, more tonnage would pass through the Soo Locks in a single year than through the Panama and Suez Canals combined.

The locks were expanded repeatedly as the ore carriers grew larger. The Poe Lock, completed in nineteen sixty-eight, accommodates the thousand-foot vessels, ships longer than the Empire State Building is tall, that now carry iron ore and limestone and grain across the lakes. Several locks have operated at the site over the years, though only two carry most of today's traffic.

The failure of any one of them for more than a few weeks, a federal study concluded, would trigger cascading shortages in American steel production within months. Lake Superior is locked in ice from December through April. When the locks reopen each spring, usually around the end of March, it marks the resumption of a shipping season that has run continuously, with those winter interruptions, for over a hundred and seventy years.