Things were different 100 years ago. Today that wouldn't happen, but by the same token that shouldn't invalidate a deal that was concluded 120 or 150 years ago.
Boozy if I recall correctly theres a peice of the St Clair river thats the same. The land owner has deeded rights (for what ever reason) that extend out into the river. It may as well be fenced off from what I've been told and theres been so much trouble in the past, the cops do repsond to calls.. So with regards to "navigable" the St Clair (which gets tankers up it) trumps the bog by a long shot.
As I said, the bog isn't the only place. One day the land will change hands and when the deed is transferred the "right" to the bed goes "poof"...Thats my understanding atleast.