Ike is right. Nothing was lost. The issue of navigability in this context relates only to ownership of the riverbank. In a non-navigable stream, property lines can extend to midstream--but the river itself is still a public resource (although ranchers have been known to string fences across creeks and rivers).
In a navigable waterway, the river bank up to the mean high waterline is public in most, but not all, cases. (I own Willamette Riverfront property, and my ownership goes to "the usual low waterline," grandfathered-in way back in the 19th century).
But Oregon has been conducting its own crusade to establish public ownership of the riverbanks throughout the state, using the navigability of the waterway as the easiest way to accomplish that. If they are successful, then they think they won't have to deal with trespassing complaints by riverfront property owners.
In reality, it only creates MORE trespassing complaints, because it is impossible for passers-by to know where the "mean high waterline" is. Oregon actually spends many, many thousands of taxpayer dollars sending a Department of Transportation aerial photographer all over the state to photograph rivers at high water, so that they can mediate trespassing disputes.