Diving in any river with active shipping is not without its risks. especially where the shipping channels have to be dredged just to keep them deep enough for the traffic.
Where I hated doing work diving was in marinas on lakes. Boat owners can be some of the filthiest humans on the planet when it comes to disposing things from their boats while docked in their slips A lot of times the water is murky with near zero visibility and you may encounter anything from bed springs to to broken bottles. rotting sail sheets fishing lines and hooks ropes and cables and every once in a while you might actually get lucky and find someone's clothes with a wallet full of cash or a gold neckless