Last weekend, out diving for abs: We were on the California North Coast, a little port on a river. The exit from the river is a little tricky; rocks on the left, and to the seaward; a couple of washrocks to the right. You exit the river mouth paralleling the beach to the right, then crank hard over to port out past a little rock island. On the way out for the morning dive, there was a boat loaded with crab traps (well, not exactly loaded, but they had about a dozen, I'd guess) just setting out. We head north to look for a calm enough spot to freedive, ended up back out along the edge of the river mouth cove. I put the other four guys in the water, and realize I didn't bring my gloves, so I sit topside and play babysitter for the divers. As I'm watching, the crab pot boat comes back into the cove, and proceeds to drop the dozen or so pots right in the channel to get back into the river. They then anchor up, also in the middle of the channel, and crack open beers. We had to sneak around all their pots, *and* their boat, to get back in.
OTOH, we also had people move on to other spots when we were diving, to keep from infringing on "our" spot (which, IMO, was completely unnecessary, but still appreciated.) So it works both ways, I guess.