Cal. Harbors and Navigation Code § 654

(a) (1) For the purposes of this section, a “muffler” or “muffler system” is a sound suppression device or system that is designed and installed to abate the sound of exhaust gases emitted from an internal combustion engine and prevents excessive or unusual noise. (2) For the purposes of this section, an underwater through-the-propeller-hub exhaust outlet system is a muffler system. (b) A motorized recreational vessel that is operated in or upon the inland waters, or in or upon ocean waters that are within one mile of the coastline of the state shall be equipped at all times with a muffler or a muffler system that is all of the following: (1) In good working condition. (2) In constant operation. (3) Installed in a manner that effectively brings the vessel into compliance with Section 654.05. (c) This section does not apply to motorized recreational vessels competing under a local public entity or United States Coast Guard permit in a regatta, in a boat race, while on trial runs, or while on official trials for speed records during the time and in the designated area authorized by the permit. In addition, this section does not apply to motorized recreational vessels preparing for a race or regatta if authorized by a permit issued by the local entity having jurisdiction over the area where the preparations occur. (d) This section shall become operative on January 1, 2005.