A week on the Texas coast usually means sunrise walks, sandcastles, and long afternoons in the surf. The Gulf of Mexico looks friendly most days, but it hides one hazard that catches even confident swimmers off guard. Knowing about rip currents on Mustang Island takes a few minutes to learn and can make the difference between a great vacation and a frightening one. The island runs from Port Aransas down toward Corpus Christi and Padre Island, and not every mile of its beach