The flag set up in Australia on patrolled beaches marks a zone where swimmers and body surfers can swim . The area is selected by lifeguards where there surf is the safest that day for swimmers.
Marked by red and yellow flags, on either side of those flags is a buffer zone marked by blue flags beyond which surfcraft are allowed.
Crossed red and yellow flags means the beach is closed and unsafe for swimming.
Bondi is a dangerous beach as it is Sydney's beach closest to the CBD, it has been publicised ( wrongly) as Australia's iconic beach so every non aware tourist goes there for their Australian surf experience.
Chaos ensues, there is a rip called the "back packer" because it is right in front of the hostel in spite of signs in many languages in they go and out they go!
Often the same people are rescued several times. There are several surf schools in Bondi, the beach can have thousands of swimmer, learner surfers, self clueless dunker. Drug. And alcohol effected people. Perverts trolling the crowd, thieves.
Bondi is a beach that focuses southerly swell and can be dangerous beyond the crowd.
North Bondi is swim and soft boards yes but again flags are put up here for a safer swimming area.
Australian beaches do not do a blackball like the US, patrolled beaches usually set up during business hours on less frenetic beaches and longer hour at Bondi. Outside the cities and big towns outside of weekends in summer, beaches are self policing and self safety.
Aerial and drone surveillance and buoys are doing shark checks somewhat. Almost every beach has a surf lifesaving club but only patrol summer weekend. Fortunately the lifesavers are guys that also like to hang around the beach and might spot a problem and save someone.
I've taken up troll hunting just for fun, instead of a rifle I'll just use a pun! 冲浪爷爷