The United States Lifesaving Association along with the International Lifesaving Federation has developed a flag warning system that has been utilized by coastal communities worldwide to inform swimmers of potential water hazards.  Beach warning flags are posted at many beaches and surf conditions are monitored throughout the day.

The flags provide a general warning, but they do not let you know if there are rip currents. A rip current is a powerful narrow channel that flows out away from the beach. It is flowing so quickly that even the strongest swimmer cannot swim against it. The only way to get out of a rip current is to swim perpendicular to shore.

Flag colors are red, yellow, green, blue or dark purple.

RED FLAGS:
The red flag is the most serious and lets swimmers know that there are hazards in the water. 

DOUBLE RED FLAG: Water Closed to Public
Conditions are too dangerous for even the strongest swimmer. Red flags signify a strong undertow or rough surf.

ONE RED FLAG: High Hazard
The surf is high or there are dangerous currents.  Swimming is not recommended; however, you can still swim if there is one red flag, but you should use extreme caution and only go in if you are a strong swimmer.

RED FLAG with a line through Swimmer: Swimming Prohibited                                 

This flag has the same meaning as the double red flag.

YELLOW FLAG: Caution – Medium Hazard
Ocean conditions may be rough and there is the potential for high surf, dangerous undertows, rocks, a sudden drop off, or a high population of bait fish that may attract predators. Children or swimmers that are not as strong should use a lifejacket, in case they get caught in the current.  It is a good idea to swim where lifeguards are present.

GREEN FLAG: Low Hazard
The ocean is unpredictable, so even though it is considered safe to swim, you should still use caution. There could be rip currents or other unexpected dangers present.

DARK BLUE or PURPLE FLAG: Dangerous Marine Life
(usually flown with a Red or Yellow Flag)
This flag indicates that sharks, jellyfish, or other dangerous marine life have been spotted in the area.  It may fly alone or with another colored flag.  When swimming, be on the lookout for marine life and stay close to shore.

REGIONAL FLAGS:  Related to activities on that particular beach.                                 

There may be a flag showing where surfing, snorkeling or other activities are either allowed or prohibited.

For more travel insight, check out my book:

Know Before You Go: Traveling the U.S. and Abroad