Cal. Harb. & Nav. Code § 658.7

(a) Failure of the operator of a vessel involved in towing a skier to display or cause to be displayed a ski flag, as described in subdivision (a) of Section 7009 of Title 14 of the California Code of Regulations, to indicate any of the following conditions, is an infraction punishable by a fine not exceeding fifteen dollars ($15):
1. (1) A downed skier.
2. (2) A skier in the water preparing to ski.
3. (3) A ski line extended from the vessel.
4. (4) A ski in the water in the vicinity of the vessel.
(b) Subdivision (a) does not apply to a performer engaged in a professional exhibition or a person engaged in a regatta, vessel or water ski race or competition, or other marine event authorized pursuant to Section 268.