One type of rip current is a topographic rip. These are found next to fixed features such as headlands, groynes and jetties. Basically the waves push water along the beach, it hits the structure and is forced out to sea.

I had no idea rips were an issue in South Korea and this picture is amazing. You can clearly see the rip from the amount of people on inflatable rafts who were carried along the beach in the feeder current and out in the rip itself!

The big 'swim parallel' or 'stay afloat' debate about what to do when stuck in a rip is still going. So Surf Life Saving Australia graciously provided myself and some colleagues at the University of New South Wales some funding to run an experiment at Bondi over a few days in September.

This is the best picture of rip currents I've ever seen.

If you go to Noosa, you'll also find a pretty strong longshore current flowing to the north. You wouldn't get very far because you'd hit the groyne in the foreground of this picture.

The English lifeguards (run by the RNLI) are pretty proactive, constantly moving the flags and getting on the loud hailer telling people where to move as conditions change with the tide.

Summer is approaching in the Northern Hemisphere which means beach time and if you've ever been to France in the summer, the beaches are packed.

One thing to note about rips like the one in this picture is that most of the water that enters rips enters from the SIDE by draining off the sand bar.

This picture was taken in April 1994 during my PhD fieldwork at Sydney's most northernmost beach...Palm Beach.

This is cool. People are starting to send me pictures of rips from overseas. This one was taken and sent by Andrew Ross, an Australian ex-pat now living in the Pacific Northwest.

So this is what the most common type of rip looks like in Australia....a dark gap between breaking waves.

These pictures are from Constantine Bay, rated as one of the most dangerous swimming beaches in the UK in terms of rips.