33 CFR 95.020 : Navigation And Navigable Waters (§ 1.01-1 To Parts 404-499) — (§ 1.01-1 To Parts 121-124) — Coast Guard, Department Of Homeland Security (§ 1.01-1 To Parts 121-124) — Vessel Operating Regulations (§ 95.001 To Subpart B) — Operating A Vessel While Under The Influence Of Alcohol Or A Dangerous Drug (§ 95.001 To § 95.050) — Standard for under the influence of alcohol or a dangerous drug.

An individual is under the influence of alcohol or a dangerous drug when:

(a) The individual is operating a recreational vessel and has a Blood Alcohol Concentration (BAC) level of .08 percent or more, by weight, in their blood;

(b) The individual is operating a vessel other than a recreational vessel and has an alcohol concentration of .04 percent by weight or more in their blood; or,

(c) The individual is operating any vessel and the effect of the intoxicant(s) consumed by the individual on the person's manner, disposition, speech, muscular movement, general appearance or behavior is apparent by observation.