Boating Under the Influence (BUI): The Law, the Limits and How to Plan a Sober Skipper

Under the Coast Guard's BUI rule (33 CFR 95.020), a person operating a recreational boat is under the influence if:

• their blood alcohol concentration (BAC) is 0.08% or more, or
• the effect of alcohol or drugs is apparent by observation: their manner, speech, movement, appearance or behavior shows it.

That second part matters: you can be charged below 0.08 if you're visibly impaired. For commercial vessels the federal limit is lower, 0.04%. NASBLA's Operation Dry Water campaign puts it simply: the federal legal limit for operating a boat is 0.08.

States enforce their own BUI laws on their waters, and the Coast Guard and states cooperate. Federal rules say that where a state has set its own BAC level for boating, that level applies within the state instead of the federal 0.08 (33 CFR 95.025). States may also have stricter limits for young operators. Look up your state's BUI law on its boating agency site or through NASBLA's state laws page.

Federally, a person is operating a recreational boat if they have an essential role in its operation while underway, including navigating or controlling the engine (33 CFR 95.015). Swapping seats with a sober friend after you see a patrol boat doesn't erase what officers already saw. Some state laws also cover people towing skiers or operating PWCs and paddlecraft; check yours.

The Coast Guard explains that sun, wind, noise, vibration, spray and motion are "stressors" that cause fatigue and speed up impairment, so a boat operator is likely to become impaired more quickly than a driver, drink for drink. NASBLA's Operation Dry Water adds that these stressors intensify the effects of alcohol, drugs and some medications. Alcohol also:

• slows reaction time and dulls judgment, balance and coordination
• reduces peripheral and night vision, depth perception and the ability to tell red from green (navigation lights and buoys)
• can make a person who falls in unable to tell up from down
• creates a false sense of warmth, raising the risk from cold water (see our cold-weather guide)

The Coast Guard says most recreational boaters average only about 110 hours on the water a year, so they have less experience to fall back on than they do in a car.

The Coast Guard publishes a chart of approximate BAC by drinks and body weight, but it warns there is no safe threshold for drinking and operating a boat. Medications, fatigue, food and heat all change how alcohol affects you. If you stop for lunch and have a drink, the Coast Guard suggests waiting a reasonable time, at least about an hour per drink, before operating, and the safest choice is no alcohol for the operator at all.

• Decide at the dock who will run the boat all day, and that person drinks nothing.
• The designated skipper should be qualified: old enough and holding any boater education card your state requires (see our education card guide).
• Make sure at least one other sober adult knows how to stop the engine and call for help (our passenger briefing guide covers this).
• Keep the key and the engine cut-off lanyard or fob with the designated skipper.

The Coast Guard's tips: bring plenty of water, sodas, iced tea, lemonade or non-alcoholic beer, plus food and snacks; dress to stay cool; and plan a reasonable trip length because people tire faster on the water. If you want a party, plan it ashore at the dock, a picnic area or your backyard, with time between the fun and getting back in the car or boat.

Passenger drinking isn't illegal in many places, but it's dangerous. The Coast Guard and NASBLA both note that intoxicated passengers are at risk of slips, falls overboard and injuries. Set house rules in your pre-departure briefing:

• Life jackets on for anyone who's been drinking, especially near the rails or when swimming
• No riding on the bow, gunwales or swim platform
• No swimming after drinking without someone sober watching and the engines off
• Kids are supervised by a sober adult

Coast Guard and state officers can stop and board recreational boats. If they suspect impairment:

• They may run field sobriety tests. On the water these are often seated tests designed for a moving boat (NASBLA trains officers in a seated standardized field sobriety test).
• They may ask for a chemical test (breath, blood or other) when there's reasonable cause, such as being involved in an accident or suspected of violating the BUI standard (33 CFR 95.035).
• When the Coast Guard decides an operator is impaired, it can terminate the voyage: the boat is taken to a mooring by the Coast Guard or a competent, sober person aboard, and the operator may be arrested, held until sober, or turned over to state or local police.

Most states have implied consent laws for boating: by operating a boat on state waters, you're considered to have agreed to a chemical test if an officer has lawful grounds to ask. Refusing can bring its own penalties, which in some states can include losing your boating privileges or even affect your driver license. Under the federal rule, if you refuse a test directed by an officer with reasonable cause, the refusal can be used as evidence in an administrative proceeding, and you're presumed to be under the influence (33 CFR 95.040). Each state's process differs; read your state's law.

• Federal: 46 U.S.C. 2302(c) makes BUI either a civil penalty or a class A misdemeanor. The statute says up to $5,000; the Coast Guard's inflation-adjusted maximum in 33 CFR 27.3 is currently $9,624.
• State: penalties vary but, as the Coast Guard and NASBLA describe, can include large fines, jail, loss of boat operating privileges and, in some states, an effect on your driver license. One example: the Tennessee Wildlife Resources Agency says a BAC of 0.08% or higher is illegal on Tennessee waters, the same as for driving, and penalties may include fines, jail, boat impoundment and loss of boat driving privileges. Its game wardens made 24 BUI arrests over the 2025 Fourth of July weekend alone.
• After an accident: if someone is hurt or killed, the charges become much more serious. You may also face civil lawsuits, and your insurer may deny or fight the claim.

If the operator is impaired, the safest move is to stop, anchor or tie up, and wait or get a sober, qualified person to take over. If no one aboard is fit to operate, call TowBoatUS, Sea Tow or a friend with a boat to come get you; it's far cheaper than an accident. If you see an impaired boater endangering others, report it on VHF 16 or by calling 911.