Rip tide, also called rip current or (incorrectly) undertow, is caused by strong on-shore winds. They occur periodically when conditions are right and do not last long. The wind causes the water to pile-up (literally, although the water pile up is not visible) against the shore. Where there are slightly deeper channels in the sea floor, or where there is a gap between sand bars on the ocean floor, the water rushes back out to sea.

A rip tide can sometimes be identified from shore due to sand kicked up from the bottom giving an area of the ocean a brownish colour, or an area of foamy, choppy water, though these signs are usually only present at large rip tides. Sometimes, semi-permanent rip tides may exist near permanent fixtures such as piers.

If you are caught in a rip tide, trying to swim directly back to shore will only tire you out quickly and completely. You will move with the rip tide away from shore until you reach the it's natural point of dissipation (called the head). The best way out of a rip tide is to swim parallel to shore until you no longer feel the current pulling you then swim straight for shore, or wait until you reach the head then swim diagonally toward the shore away from the rip tide.

Approximately 80% of all rescues by beach lifeguards involve swimmers caught in rip tides.