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Safe Water Marker - Obstruction Marker - Mooring Buoys - Divers’ Flag - Alpha Flag

Safe Water Marker

Safe ater marker

These are white with red vertical stripes and indicate unobstructed water on all sides. They mark mid-channels or fairways and may be passed on either side. 

Obstruction Marker

Obstruction Marker

These are white with black vertical stripes and indicate an obstruction to navigation. You should not pass between these buoys and the shore.

Mooring Buoy

Mooring buoy

These are white with a blue horizontal band. They are usually placed in marinas and other areas where vessels are allowed to anchor. These are the only buoys you may legally tie up to.

Western Rivers System

Found only on the Mississippi River and its tributaries as defined by the U.S. Coast Guard in Rule 3 of the COLREGs. These aids to navigation are not numbered as in IALA-B system. Numbers indicate mileage from a fixed point. Lights on green aids show a single-flash which may be green or white. Lights on red aids show a group-flash which may be red or white. Diamond-shaped crossing dayboards, red or green as appropriate, are used to indicate where the river channel crosses one bank to the other.

Uniform State Waterway Marking System (USWMS)

On bodies of water wholly within state boundaries and not navigable to the sea, each state is responsible for establishing and maintaining aids to navigation. A uniform system of aids and regulatory markers has been agreed to by all states.

Some informational/warning flags you might see include:

Divers’ Flag indicates that scuba divers or snorkelers are operating in the area. Stay well clear of this flag. Many states have specific distance-away requirements from 100 to 300 feet. Check your state regulations.

Rigid Alpha Flag is flown by a vessel engaged in diving operations. This flag does not substitute for the diver-down flag above in states that require the diver-down flag. You will usually see both flags in use. The alpha flag indicates that the vessel is restricted in ability to maneuver, in this case due to the nature of its work. 

diving flag alpha

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