Here's the rule on noise, straight from the California Dept. Of Boating & Waterways;
MUFFLING SYSTEMS
Any motorboat operated on the inland waters of this state, or coastal waters
up to one mile from shore, must be muffled or otherwise prevented from
exceeding the following noise levels when measured by the Stationary Sound
Level Measurement Procedure for Pleasure Motorboats (SAE J2005):
90 dB (A) for engines manufactured before January 1, 1993.
88 dB (A) for engines manufactured on or after January 1, 1993.
All motorboat noises levels must be below 75 dB (A) when measured by the
Shoreline Sound Level Measurement Procedure (SAE J1970).
Authorities generally agree that unbaffled exhaust pipes (stacks) do not meet
any of the above noise level requirements.
