So the U.S. Army Corps of Engineers, Detroit District, is doing their annual winter maintenance at the Soo Locks, which they do each January through March, as they prepare for the 2020 shipping season; which means we get an inside look at the lock system.

During the winter maintenance season, they drain all the water from the locks and then go down into the lock system to clean it out and repair what ails it.

This year the Corps of Engineers posted on Facebook that they’ve already cleared out over 600,000 pounds of debris that was either left by the ships throughout the last season or pulled in with the ships, in just the Poe Lock.

According to MLive,

they cleared out a lot of rocks as well as bolts, pieces of rebar, and tools that had been accidentally dropped into the water by topside work crews during the shipping season

It's interesting to see just how big some of the debris is.  Look at the picture below, of them loading a giant yellow bucket.  See how big the red Jacobsville sandstone rocks are.  Those didn't fall off a ship... maybe some did, but rocks that size get pulled into the locks with the current as they raise and lower the water level or with ships, as their propeller wash pulls in the rocks too; As one of the comments from the U.S. Army Corps of Engineers on the Facebook post said: "This is why the locks are designed with debris pits at the gates, to help catch the rocks and other items that wash in."

MLive says all repairs to and cleaning of the Soo Locks will be done by March 25th, the opening of the 2020 Great Lakes Shipping Season in which around 4,500 ships will pass through the lock system.