California Code, Public Resources Code - PRC § 9301

(a) The board of directors shall consist of five, seven, or nine directors. The number of directors may be changed by resolution adopted by a majority of the members of the board of directors after publication of notice of the intended change at least once in a newspaper of general circulation published in each county in which the district is located.

(b) If the number of directors is increased, the new positions shall be treated as vacancies and shall be filled as provided in Section 9317, except that if the board of directors is appointed as provided in subdivision (b) of Section 9314, then the new positions shall be filled in the same manner pursuant to Section 9316. If the number of directors is decreased, the terms of the directors in office on the date of the resolution adopted pursuant to subdivision (a) shall not be reduced.

(c) The directors first elected shall take office immediately upon qualifying.