It's the same all over. Locally we have a river with a long and interesting history of long boat, barge and steam boat traffic. The thing is if you find something interesting or historically significant that sunk or fell off a boat or dock, the local governments claim it 100% as their own. That removes any incentive for divers to report the find so that an investigation of the site and possible acheological excavation could be done (assuming funding could be found). And the reality is that as the river winds back and forth covering and uncovering artifacts, if divers do not find them, they will not be found.