I never knew these existed until I went to Australia and saw them all over.
They have pools that are right on the beach. At first I thought it was crazy, but I quickly grew fond of the idea. They're just saltwater pools that allow people to swim laps at the beach without fighting waves or getting swallowed by a whale.
The only downside was in Cronulla, the waves were huge and breaking over the wall of the pool, turning it into a concrete deathtrap. So be advised, don't swim in the beach pools if it's double overhead.
California, take notes.