In most states, a vessel must stay at least 100 to 300 feet away from a displayed diver-down flag in open water, and roughly 50 to 100 feet away in rivers, inlets, and navigation channels. Within that buffer, you’re required to drop to idle speed. The exact figure depends on which state’s waters you’re in and the type of waterway, so how far a vessel must stay from a diver-down flag is really two numbers, not one.
The Two Flags You Might See
Two different flags mean divers are in the water, and boaters should treat them the same way.
The recreational diver-down flag is a red rectangle with a white diagonal stripe running from the upper left to the lower right corner. This is what recreational divers and snorkelers fly from a boat or tow behind them on a float, and it’s the flag most state boating laws point to when they set distance and speed rules.
The Alpha flag is a blue-and-white swallow-tailed pennant used under international navigation rules. On federally controlled waters, vessels engaged in diving operations must fly a rigid replica of the Alpha flag at least one meter tall, visible from all directions.1eCFR. 33 CFR 83.27 – Vessels Not Under Command or Restricted in Their Ability to Maneuver It tells other boats that the displaying vessel can’t maneuver freely because it has divers below. You’ll see it most often on commercial dive boats and research vessels.2National Oceanic and Atmospheric Administration. Guidance to NOAA Diving Units and NOAA Ships on the Use of Warning Signals During Diving
Many dive boats fly both at once. If you see either flag, slow down and give the area a wide margin.
Distance Rules by Waterway Type
There is no single federal distance that governs the red-and-white diver-down flag on all waters. Each state sets its own numbers, and they range from about 50 feet up to 300 feet depending on the state and where you are. On federally controlled waters where the Alpha flag applies, vessels should stay as far away as is reasonable and prudent for the circumstances.
Most state rules follow a two-tier pattern:
- Open water: boats must stay 100 to 300 feet away from the flag and operate at idle speed inside that zone.
- Rivers, inlets, and navigation channels: the buffer usually shrinks to 50 to 100 feet, because the waterway may not physically permit 300 feet of clearance. Idle speed still applies.
Check the specific rule for the state whose waters you’re on. The tiers are consistent, but the exact numbers are not.
What Idle Speed Actually Means
Idle speed is the slowest speed at which the boat can move while the operator still maintains steering control. In practice that usually means the throttle at its lowest forward setting. The goal is to minimize your wake and leave yourself time to react if a diver surfaces unexpectedly.
Slowing down is the legal minimum, not the whole job. Scan the water for bubbles, surface marker buoys, and any sign a diver may be ascending away from the flag. Divers don’t always come up right next to the flag, especially in current. Passing between a diver-down flag and the nearest shoreline is particularly risky, because that corridor is where divers commonly enter and exit the water.
Night and Low Visibility
A flag is useless in the dark, so the signals change. Federal guidance for government diving operations calls for both the diver-down flag and the Alpha flag to be illuminated during night diving.2National Oceanic and Atmospheric Administration. Guidance to NOAA Diving Units and NOAA Ships on the Use of Warning Signals During Diving Some states require the flag to be lit well enough to be seen from at least 100 feet away.
Vessels engaged in diving operations must also show the navigation lights prescribed by Rule 27: three all-round lights in a vertical line, with the top and bottom red and the middle white.1eCFR. 33 CFR 83.27 – Vessels Not Under Command or Restricted in Their Ability to Maneuver At night, seeing that red-white-red vertical pattern means the same thing as a diver-down flag by day. Slow down and stay well clear.
When You Can Come Closer
A few situations allow a vessel inside the normal buffer.
The dive boat itself is one. The vessel directly supporting the divers is going to be within the restricted distance by definition, and the law accounts for that.
Law enforcement and search-and-rescue vessels are exempt when actively performing their duties. An emergency may allow another vessel to approach closer than the legally required distance, but the operator still has to proceed at idle speed and exercise extreme caution.
Narrow waterways sometimes make the full distance physically impossible. That is not permission to pass at cruising speed. The expectation is that you slow to the minimum speed needed to hold steering and transit the area as carefully as you can. These exceptions cover genuine impracticality, not convenience.
Fines for Ignoring a Diver-Down Flag
Fines are set by state law and vary. A first offense is commonly a non-criminal infraction with a fine in the low hundreds of dollars. Repeat violations within a set window escalate: second and third offenses can bring $250 to $500, and habitual offenders may face $1,000 or more. Some states classify repeat or egregious violations as misdemeanors, which carry consequences beyond the fine.
Those regulatory penalties are the smaller half of the picture.
Civil Liability If You Injure a Diver
If a boat operator speeds through a marked dive zone and injures or kills a diver, the regulatory fine is the least of it. The diver or the diver’s family can bring a personal injury or wrongful death suit, and damages in propeller-strike cases regularly reach six or seven figures once medical costs, lost income, rehabilitation, and pain and suffering are counted.
The legal question usually turns on whether the operator acted reasonably under the circumstances. Ignoring a clearly displayed diver-down flag is strong evidence of negligence, and depending on conditions it can look reckless. The flag existed to warn the operator, the operator was legally required to slow down and maintain distance, and the operator chose not to. That is a hard position to defend.
Reporting a Collision With a Diver
A collision with a diver triggers a mandatory federal report. The operator must file a written boating accident report when the incident causes a death, an injury requiring medical treatment beyond first aid, the disappearance of a person from the vessel, or property damage of $2,000 or more.3eCFR. 33 CFR 173.55 – Report of Casualty or Accident
Deadlines are short. If someone dies within 24 hours of the incident or is injured beyond first aid, the report is due within 48 hours. For qualifying property damage without death or serious injury, the deadline is 10 days.3eCFR. 33 CFR 173.55 – Report of Casualty or Accident If the operator can’t file, the vessel’s owner is responsible. Failing to file is a separate violation on top of anything stemming from the incident itself.