What’s this flag for....

It’s great to see the lifeguards back patrolling daily as the school holidays start. We’re used to seeing their red and yellow flags, they delineate swimming and bathing etc areas “swim between flags.” The new black and white flags appeared today - apparently they mark out the area for surf board users etc. Their loud hailer was in use today; warning boys jumping off the pier that the water level was too low at this point of the tide.