One of the additional problems with fisheries and navigable waters power is that they have been read down by the courts. If it doesn't look like fish, even though you put it in the Fisheries Act it doesn't mean the courts will accept it. There were a couple of cases in the early 1980s that addressed that. One dealt with a provision in the Fisheries Act that says you can't throw your trash in the water. I think it was primarily aimed at logging. It was struck down by the courts--I'm sure you're aware of Fowler--precisely because it wasn't linked directly to harm to fish.
So the courts have been relatively jealous about ultimately protecting provincial resource management policies where the federal government seems to be going beyond the strict confines of the heads of power it's been given.