In my view, all of it.
As you know, vessels have been using the St. Lawrence River to transport goods since the 1800s and even before. Human manipulation of the river goes back to 1850 or 1860, and includes dredging, as I mentioned. Clearly, that may not be as serious of a problem. The experts will tell you that.
Dams, reservoirs and booms were built and are still there. Because of the many things humans have done to the river, shoreline erosion is much worse today than in the past.
Here's something I've wondered about, and I'll put the question to you. If, as a community, we've benefited from using the river to transport goods, wouldn't it be appropriate—necessary, even—to consider compensating the people who today are experiencing the negative consequences of that use?
If we can't do that, as a society, we aren't worth our salt.