Cal. Water Code § 75621

A determination made by the district pursuant to Section 75619 shall be conclusive on all persons having an interest in the water-producing facility involved, and the ground water charge, and the interest and penalties thereon, shall be paid forthwith, unless any such person files with the board, within 10 days after the mailing of the notice of the determination, a written protest setting forth the ground or grounds for protesting the amount of production so fixed.