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A red flag with a white diagonal stripe is a diver-down flag: it warns that divers may be in the water nearby. Keep clear and reduce speed as local rules require. It is not a distress signal, and it is not interchangeable with the blue-and-white Code Flag Alpha.
What the red-and-white flag means
The red rectangle or square crossed by a white diagonal stripe is a diver-down warning used in North American recreational diving. It alerts boaters to the presence of divers in the water around a dive site; the flag does not indicate that the boat itself is in distress or unable to maneuver.
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The U.S. Coast Guard says the traditional red-and-white diver’s flag remains distinct from Code Flag Alpha. In its Local Notice to Mariners dated April 13, 2025, the Coast Guard states of the mistaken belief that Alpha replaced the diver’s flag: “This impression is incorrect.”
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How it differs from Code Flag Alpha
| Signal | Appearance | Meaning | What to do |
|---|---|---|---|
| Diver-down flag | Red rectangle or square with a white diagonal stripe | Divers may be in the water nearby | Keep clear; follow local distance and speed rules. |
| Code Flag Alpha | Blue and white international code flag | A vessel is restricted in its ability to maneuver during applicable diving operations | Treat it as a vessel navigation signal, not as a substitute for the diver-down warning. |
Under U.S. Coast Guard Navigation Rule 27(e), a vessel engaged in diving operations that cannot practically show all the signals specified elsewhere in Rule 27 because of its size displays three all-round lights in a vertical line—red at top and bottom, white in the middle—and a rigid International Code Flag A at least one meter high and visible all around. This is a specific vessel-signal requirement; it does not make Alpha and the red-and-white diver flag interchangeable.
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What to do when you see a diver-down flag
- Keep well clear of the marked area and avoid passing between the flag and the likely dive site if doing so could put divers at risk.
- Reduce speed and maintain awareness of people in the water. Follow the requirements for the waterway you are using.
- Do not assume a single distance applies everywhere. Check the rules for your state or local jurisdiction.
For example, the Florida Fish and Wildlife Conservation Commission says boaters must make reasonable efforts to stay 300 feet away in open water and 100 feet away in rivers, inlets, or navigation channels. Within those distances, boaters must slow to idle speed. These are Florida requirements, not a nationwide distance standard.
The Pennsylvania Fish and Boat Commission likewise advises boaters to remain at least 100 feet from areas marked by either diving sign. That is a Pennsylvania example, not a universal rule.
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Display rules vary by location
Florida’s requirements illustrate why divers and boaters should check the rules where they are on the water. The Florida FWC says its diver-down rules apply when a person is wholly or partly submerged while using a face mask and snorkel or underwater breathing apparatus. The warning device must show a red rectangle or square with a white diagonal stripe.
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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problems- Minimum dimensions in Florida: 12 by 12 inches for a symbol displayed on the water, and 20 by 24 inches for one displayed on a vessel.
- Vessel placement: Display it at the highest point where it is unobstructed in every direction.
- Flag construction: The symbol must appear on both faces. The flag must be stiffened or made to remain extended even when there is little or no wind.
- When to display: Florida says the device may not be displayed when divers are out of the water.
Divers Alert Network’s Safe Boating Guidelines recommend matching minimum dimensions of 20 by 24 inches on a vessel and 12 by 12 inches on a buoy, and advise flying the vessel flag above the vessel’s highest point. DAN also advises keeping flags stiff, unfurled, and in recognizable condition. Its safety guidance does not replace local law; Florida’s legal display requirements apply in Florida, and other jurisdictions may differ.
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