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.
references:
http://205.67.213.10/Information/Ripcurrent/RIP.htm, http://www.ci.imperial-beach.ca.us/riptide.htm, http://www.sannet.gov/lifeguards/safety/bchsafe.shtml