Lanikai Beach, HI
Credit: Steven Greaves / Getty Images

This mile-long beach in the small town of Kailua, on Oahu, is "the most picturesque beach in the country," Leatherman says. The nearby Mokulua Islands and coral reefs with tropical fish are part of the appeal. So, what makes Lanikai a great swimming spot? The water is five feet deep for half a mile offshore. That means that there are essentially no waves.

"It's a very small beach, but it's a beautiful beach," Leatherman says. "I love going there."