The flags signify the potential for strong rip currents.
"A red flag is flown when conditions are determined to be out of the ordinary, such as presence of strong wind, strong current or large surf. Adult swimmers should stay in water no more than waist deep and non-swimmers and children should be kept along the surf line," according to the Galveston Island Beach Patrol.
Updating conditions on Galveston Island: red flag warnings are now in effect pic.twitter.com/hHpQ6x4aE5— Jeff Ehling (@JeffEhlingABC13) July 3, 2017
Under these conditions, beach patrol is urging beachgoers to swim near lifeguard stations and to stay out of the water, specifically near San Luis Pass.
RELATED: Body of 19-year-old fisherman who went missing at San Luis Pass found
The use of life jackets is also urged for non-swimmers.
If you are caught in a rip current, lifeguards advise swimmers not to fight to get out of one and to instead relax and float. Eventually, you will be pushed back ashore.
In addition, swimmers should swim parallel to the shore if possible. Others who see someone in distress are also urged not to go into the current. A flotation device should be thrown to them instead.
Of course, the best advice to swimmers is to avoid the potentially deadly currents altogether and to stay away from rocks and piers.
Extra patrols are being deployed, but swimming near lifeguard stands is highly recommended during the warnings.
For a closer look at the flag warning system, visit this page.
WATCH: How to survive a rip current
Report a typo to the ABC13 staff