It has been several decades since my studies of isostatic rebound, but as I remember, what is happening is that the rebound further south is pretty much done in comparison to further north. The result is the land is slowly tilting with areas to the north getting higher which tends to drain Huron more. Not saying that dredging has not had an impact, but if it did have a huge impact then Erie would be much fuller than it is.
Heading back to Lake Ontario for this summer. Now in Bermuda and heading to Long Island Sound in the first week in May. Then on to the Hudson and the Erie Canal.