This is what makes the world go round. It's not just a Great Lakes "problem." Weather has Always been cyclical, and really is uncontrolled by all the hand wringers..
Last year central Europe had a very dry Spring/Summer. That dropped the water levels in the Danube, Maine, and to a lesser extent the Rhine. This year, mostly back to normal, to above normal levels. Really screwed up the river cruise business with the low water. The controlling river authority(s) closed portions of the rivers, at various times.
Passau Germany sits at the confluence of three rivers, and had the worst floods in 500 years, in 2013. Last year high and dry, this year back to normal. All these rivers are controlled by a series of locks to facilitate barge transportation, and to a lesser extent river cruise ships but there's only so much of nature that ever really gets "controlled." At least Passau had the benefit of 500+ years of weather/river data to compare. While We're still falling back on geology to try to figure it out.