Had heard people talking about "bluebottles" spoiling beach trips further up the coast, and there were loads of these at Lyall bay yesterday (we weren't there to swim so nothing spoiled).
Where I'm from bluebottles are a large fly but reading on Wikipedia these are actually the same species as the famous Portuguese Man O'War (https://en.m.wikipedia.org/wiki/Portuguese_man_o'_war).
That's them. Nasty sting indeed - my niece got hit the other day swimming at our local beach here on the West Coast (S.I.)