A Rip Current
Most people won't actually try to run away from a rip current; they probably hope to outswim it. An unexpectedly strong current that forms at low spots or breaks in a sandbar, a rip current can move at a speed of up to 8 feet (2.4 meters) per second. Swimming toward shore might be your first move when a leisurely dip in the ocean is threatened by a powerful current channel, but it could also be your last [sources: National Ocean Service, Popular Mechanics].
Experts say that the currents are tough to outswim, and those who try to do so may become fatigued (and risk drowning) before reaching dry land. Instead, swim parallel to the riptide. It's likely to be less than 100 feet (30 meters) wide. If that doesn't work, lie flat on your back and let the current take you away from shore until you've passed beyond it. Then try swimming around it or to shore [sources: National Ocean Service, Popular Mechanics].