Legal Question in Administrative Law in California

Re: police procedure

Probably not; the right to do invasive tests has to do with arrest and probable cause, and since merely being an intoxicated passenger is not illegal (as far as I can tell after a little research), there would seem to be a lack of probable cause and the test would be a 4th Amendment violation.

However, this has to be a qualified "probably not" answer because if there is a reasonable suspicion that the supposed passenger had been operating the vessel, then the arrest and search could be justified. In most boats, it is all too easy for the operator and the passenger(s) to switch roles, or for them to share operating roles at the same time.

It's also possible that the blood test was taken because of suspicion of use of controlled substances, not alcohol; for example, if there were the odor of marijuana or drug paraphernalia.

Finally, if the tested person were on parole or probation, the person may have relinquished their search and seizure rights as a condition thereof.