The lifeguards put them up a few days ago because there were moon jellies. I haven't seen any in the last couple of days, and anyway the moon jellies are nearly harmless. But this time of the year it's good to be on the lookout for the ones that I think are called sea nettles - look like parachutes. Those have a painful sting and usually show up in Aug, although I haven't seen any of them this year.
I did see a blue button this afternoon, but they are harmless too.