As I mentioned previously, individual marinas (supposedly) can restrict maintenance activities like in-water hull cleaning if they so choose. However, there are no statewide bans on hull cleaning anywhere in this country. In Washington, the state has limited hull cleaning to hard paints only. No ablatives can be cleaned in the water in that state. In Massachussetts, the "Clean Marina Guide" does indicate that as a Best Management Practice, in-water hull cleaning should not occur, but this is strictly a voluntary measure and does not carry the weight of law. There are any number of dive services advertising hull cleaning up and down the Massachussetts coast.
Massachusetts Clean Marina Guide
Hull Cleaning and Boat Washing | Clean Green Boating | Washington State Department of Ecology
fst - What do you see coming regarding Nor Cal regulations?