A rip current is a narrow, river-like channel of water moving away from the surf (breaking) zone and back toward sea. Rip currents can travel up to 3 mph (4.8 kph) and stretch 100 ft (30.5 m) wide. Some cease just past the breaking surf; others extend a thousand feet offshore. In some regions, the rip current, or rip tide, is a permanent feature of the sea. In other areas, one can appear suddenly or intensify after a storm or a breach in an offshore sandbar.
Rip currents are fed by long shore currents, or feeders, which flow parallel to the beach inside the surf zone . In addition to the feeder, each current consists of a neck (main channel) and a head. The neck is the point where feeder currents converge and move back out to sea through a weak spot in the breakers. The head is the widest part of the rip current. Rip currents are typically found near jetties of irregular beaches and along straight, uninterrupted beaches. Although often mistakenly called one, a rip current is not an undertow.
Telltale signs of a rip current include murkier or darker waters, changes in wave formation (large, choppier waves inside the current, calmer ones up front), and foam moving seaward.
The intense currents can pull even the most experienced swimmer into dangerously deep ocean water. Attempting to swim to safety against the current can result in exhaustion, panic, and sometimes drowning. An estimated 80% of United States lifeguard rescues are due to rip currents. Experts advise swimming parallel to shore until you surpass the current, then head toward land. Inexperienced swimmers should tread water and call for help.
See also Ocean circulation and currents; Surf zone