ABOARD THE USCGC MACKINAW -- It's minus 16 degrees on the deck of this 240-foot Coast Guard cutter.
That means it's time to go to work.
Thousand-foot freighters pass through the Great Lakes each winter, carrying with them shipments of iron ore that help fuel the steel industry. But ships like these are often no match for the ice that clots their thoroughfare.
We traveled with the 57 member crew on January 12, 2018, just three days before the Soo Locks were set to close, effectively ending the shipping season.
After loosening the Mackinaw from its moorings, we venture up through the locks, which allow boats to travel freely along the St. Mary's River at a section that otherwise drops off 21 feet.
We're on a mission to cut loose the Burns Harbor, a freighter heading to Lake Superior with a shipment of iron ore.
Each time the crew frees a boat from the icy grips of the Great Lakes this winter, they put a tally mark on the front window of the ship. If the mission was successful, the Burns Harbor would be the 47th tally mark of the winter.
They set on their course, boring past the Burns Harbor and sending shattered chards of ice to either side of the ship. They then weaved their across the ice, cutting out a lane to lead the freighter back toward the Soo Locks.
The next morning, the traffic jam continues along the Great Lakes, and it's Tom Soeltner's job to make sure it gets cleared.
He's the lock master at the Soo Locks, meaning that from his tower above the facility, armed with a radio and nautical navigation tools, he decides who comes and goes along these waterways.
Today, the Indiana Harbor, a 1000-foot freighter, is trying to work its way down the St. Mary's River.
Along with deciding when boats will pass through, Soeltner has to take into account the maintenance of the locks. Downstairs, a team of divers waits for the go ahead to get into one of the locks to do some scheduled work.
From up on high, Soeltner tries to perform an intricate ballet act with the colossal boat.
It's one of the largest ships on the Great Lakes and today, it just won't fit neatly into the locks, which are only feet wider than the ship itself.
On a good day, the Indiana Harbor could pass through the Soo Locks in about an hour. Today, with the deadline approaching to get ships through before the end of the season, it takes about three hours.
Part of the problem comes when Soeltner must let two tugs come up the locks, leaving the freighter and the cutter that guided it this far lying in wait. That made the boat get re-stuck so that it had to back up and bore through the ice again, setting it adrift from the narrow track it must cut to enter the locks.
Once the boat slips into the locks, it's easy to see why these shipping lanes get so jammed up. The hull of the boat is caked in ice.
As it passes through the locks, maintenance teams prepare for their dive.
Maintenance is the reason these locks get shut down for the winter in the first place. But even the 10 weeks they take off aren't enough to get everything done.
Finally, the freighter pushes through and heads down the St. Mary's River. The season's not over yet, but it's close. And one more shipment of iron ore has made it to its destination.