The Pacific Ocean, which gives Sydney, Australia, its iconic coastline and some of the world’s most enviable beaches ... her with red splotches on her skin. “I like how soft the sand is.

In late November, a gaggle of open-water swimmers set out from Sydney’s Bondi Beach. About 500 meters (1,600 feet) from shore, they stopped and formed a line 150 meters (about 500 feet ...