Cal. Harb. and Nav. Code § 100
Navigable waters and all streams of sufficient capacity to transport the products of the country are public ways for the purposes of navigation and of such transportation. However, the floodwaters of any navigable river, stream, slough, or other watercourse while temporarily flowing above the normal high-water mark over public or private lands outside any established banks of such river, stream, slough, or other watercourse are not navigable waters and nothing in this section shall be construed as permitting trespass on any such lands. For the purposes of this section, "floodwaters" refers to that elevation of water which occurs at extraordinary times of flood and does not mean the water elevation of ordinary annual or recurring high waters resulting from normal runoff.
Ca. Harb. and Nav. Code § 100