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What are the different kinds of currents?

If you've gone swimming in the ocean, you've probably noticed that there's often a current that drags you along the beach, parallel to the shore. This is called a longshore current. It's caused by waves that head toward the shore at an angle. Some of the energy from the waves is directed toward the beach. But some of the energy is pushed in a direction parallel to the shore, causing the current. Over time, longshore currents carrying dirt can cause islands to be built up parallel to the beach. 

Another type of current is the rip current. A narrow place between the islands or a gap in a sand bar can funnel the water heading out to sea after the waves have crashed. This works a bit like the plug in a bath -- all the water rushes out, making a current.  Swimmers need to be careful that a rip current doesn't pull them out of their depth.