Rip current
A rip current is a strong flow of water returning seaward from the shore. It is also called a "rip tide" or "riptide," or colloquially simply "rip." They occur in the world's oceans and in very large lakes such as the Great Lakes in the United States. A common misconception is that a rip occurring under the water, instead of on top—an undertow—is strong enough to drag people under the water; this is not true.Such currents can all be extremely dangerous, dragging swimmers away from the beach and leading to death by drowning when they attempt to fight the current and become exhausted.
Surviving an encounter with a rip current
It is important to never attempt to fight a rip current. One should always swim parallel to the shoreline. If you see a person caught in one, yell at them to do so. This removes the swimmer from the current, which typically occurs most strongly between sandbars. Floating until the current disperses into deeper waters is also another method of surviving such a dangerous incident, but it may leave the swimmer farther out from shore. Rip currents can be deadly for non-swimmers as well. A person standing waist deep in water can be dragged out into deeper waters. If they are unable to swim, and are not wearing a flotation device, drowning is a strong possibility.
Avoiding the shore when surf is rough (such as during high onshore winds, or when a strong hurricane is far offshore) is an advisable safety measure, as this is when very strong tides or currents are most prevalent. Posted warnings, where available, should always be heeded. Also, check the local newspaper and internet for tide timetables. (Beware, tides can be substantially different at beaches relatively close to each other.) Never go into the water without lifeguard supervision within several hours of a low tide greater than a few inches--especially at night.