I understand your point that that MT is a lot more rural and much less populated than PA.
That isn't my point at all.
However did you look at the map of streams the DCNR already considers public streambed in PA? Over 200+ streams (many smaller than Elk Creek in Erie) that the DCNR already considers public stream bed.
Most of the water on that map is a significant waterway, and while you may think that this means it's open to fishing like open water in Erie, for the water on the map I'm familiar with, I know that's not the case. There are sections of that water that are posted, and to fish through would be trespassing.
We can legally float down any body of water in the state without touching bottom.
Passage rights only concern passage. Even if you aren't anchoring, doing anything other than moving through can get out into trespass issues. Fishing certainly falls under that description.
We can legally walk streambeds within the high water mark on any small stream deemed navigable, why? Because some farmer in the early 1800's use to float produce downstream to market. But we can't walk within the high water mark of a stream where publicly funded resources are being allocated today. Doesn't make sense to me.
Are the Erie ditches navigable? No. There's your answer.
You seem to have it in your head that you can just snap your fingers, declare a stream navigable, and poof, instant access for everyone.