apparently it is not legal, nor is tubing, rafting, SUP'n and drinking, unless otherwise specified.
http://www.dbw.ca.gov/Pubs/Alcohol/ba.pdf
and vessel is defined:
(aa) "Vessel" includes every description of watercraft used or capable of being used as a means of transportation on water, except either of the following: (1) A seaplane on the water. (2) A watercraft specifically designed to operate on a permanently fixed course, the movement of which is restricted to a fixed track or arm to which the watercraft is attached or by which the watercraft is controlled.