In browsing the net, I came across these photos of the old Brighton-le-Sands swimming enclosure on Botany Bay. (National Library Collection: Picture Australia).
That got me remembering that I used to go down there in the late 1960s / early 1970s. Used to love sliding down the suspended slippery dips into the water!
There is still an enclosure there, but no longer an elevated boardwalk to jump and slide into the water from. It looks like this:
Here's a terrific pic I found of a surf carnival at the baths (date?)