Well, they have laws, and there is always civil penealties, but enforcement is beyond abysmal at times.
There are lake cops and rangers who break these rules, And if you point out that a boater broke these rules, even if you have the registration numbers from the hull, officials will often blame the divers for the problem. There was one lake in Iowa that was closed to divers due to the complaints of Cats constantly runing over dive flags. Signs had been posted, pamphlets left, and people were constantly warned, yet whenever anyone expected the laws to be enforced, it was the divers that were to blame, because they happened to be there.
So, after the divers were thrown out things were fine for a year or so, and then a catamaran ran over a 6 year old girl killing her. Suddenly everyone wanted to know why no one was enforcing rules on that lake. I'm sure they would have tried to blame us if they could have found a way.
BTW : Several rather ugly fights started after divers tried to tell boaters about the flags and the divers were told, basicly, "Who gives a damn, it's only divers!" I wasn't in any of those fights, but I'll tell you what, if anybody said they didn't care if they killed a diver to my face, I would be hard pressed to not take that personally.