Sean Cunningham/Backstage Beauty/Hearst
The first step to create this look is preventing salt water from penetrating your hair's shaft and making it brittle by spritzing towel-dried hair with an oil spray (try Davines SU Sun Protective Moisturizing Oil, $20, 866-328-4637 for store locator). It repels salt water while adding moisture, and it prevents frizzies.
Divide the hair you want to braid into two equal sections.
Start a fishtail braid by holding the right section with your right hand. Then, using your left hand, pick up a one-eighth-inch chunk of hair from the outside of the left section and cross it over to the inside of the right section.
Repeat on the other side: Hold the left section in your left hand. Use your right hand to pick up a one-eighth-inch chunk of hair from the outer right section and cross it over to the inside of the left section.
Continue picking up small sections and crossing them over until you reach the ends of your hair.
Secure with an elastic.
If you're spending a lot of time in the water, when you're back home, cleanse the oil and salt from your hair with a purifying shampoo and use a deep conditioner (try Redken UV Rescue Recovery Treat, $15, redken.com).