Every day, Lifeguards survey and mark safe swim zones by planting a red & yellow flag at the ends of the safe swim zone. During the day they shift the flags to ensure that the safe swim zone does not contain any hazardous elements.
This marks out the area of the beach constantly under observation by lifeguards. The area in between the red and yellow flags is the safe area to swim & body board.
This indicates danger. NEVER, under any circumstances, enter the water when the red flag is flying.
The danger could be - rough sea conditions; submerged rocks; submerged hazardous objects; area prone to formation of rip current; sudden drop in sea floor; presence of harmful marine creatures etc. Areas where the Black and White chequered flag is hoisted is an area where water crafts may come close to shore. You should NEVER swim or body board in such areas.
It is also recommended that even if the Black and White chequered flag is not hoisted , one should swim / bath only in the earmarked safe swim zones.