While exploring California’s more than 1,000 miles of beachfront property, we continually found ourselves drawn to beaches with sparkling blue water, ideal for such underwater activities as diving and snorkeling. Crystal clear water, however, is not always an indication of cleanliness. In fact, while we admired it from afar, we avoided swimming in Catalina’s Avalon Harbor Beach. Outfitted with some of the state’s most vibrant blue water, the snorkeling hot spot remains the most polluted beach in California.