Fish poo is the least of your worries, and the surfers aren't wearing wetsuits just to keep warm anymore. Water parks are popular in Southern California, and there are plenty to choose from between Los Angeles and the Nevada border.
Chlorine is a wonderful thing.
And if you get seriously stuck in the undertow, they can always shut it off to fish you out. It's the natural choice for Coachella Valley residents. The newest attraction is the Shark Attack, a three-man inner tube ride. And if you need a compromise, try the Lazy River ride. From I-10, take the Gene Autry exit and go south past Ramon Road.