(ca, Usa) Neighbor Rents Out Their Dock

I just moved into this neighborhood and my house was previously abandoned for a few years. In that time, my neighbors tenants I guess feel that my property belonged to them, from what I understand they used my property a lot and are now mad that I've bought the place. My neighbor rents his dock out to ~3 different boats, they park on my property, have "guests" coming all the time for short visits, fill my trash can. They're now allowing one of their homeless friends to sleep in his car in front of my house, who is shitting all over the sidewalk. Yesterday I went to walk outside and one of the tenants two dogs came rushing at me, growling at me and my dog.

I'm getting pissed and my neighbor is an older guy who seems to be retired and the entire neighborhood seems to have a massive problem with him due to these people he rents his dock out to. I know there's at least 3 house boats, and I've talked with one of them, he seems nice enough and I really wouldn't care about these tenants if they stayed off my property and left me alone, but despite only living here for ~2 months my house has been broken into twice, and I'd wager that it was these damned dock neighbors who easily know when I'm coming and going and seem to have a grudge against me for taking away their hang out spot.

Talking with my neighbor about his tenants has done nothing, and is just irritating both of us as now I'm threatening his passive and probably only source of income, and I'm tired of these people he's renting his dock out to.

A few neighbors came to talk to me as they thought these people were my renters since they park in front of my homes public parking instead of my neighbors and I told them, they weren't mine, they all seem pretty convinced that in this area living on docks is not allowed, so at this point I want to do my best to get rid of them, because talking to my neighbor is proving fruitless and his tenants seem to just ruin the neighborhood.

Who can I talk to about seeing if living on your dock is allowed in my area? Other angles anyone else can think of?