I remember seeing this chart many years ago in the Soo Locks Visitors Center. The one thing we can say of water levels on the Great Lakes is they are always fluctuating.
https://lre-wm.usace.army.mil/ForecastD ... -Graph.pdf
Being a Lake Erie boater, I have been through many cycles of high and low water levels and have adjusted my boating accordingly. So big picture, do shipping companies also consider this in their long-term planning knowing they will have years where cargo capacities can be maximized, and other years where draft will be the driving factor?