rip current
A rip current is a strong, localized, and narrow current of water that moves directly away from the shore by cutting through the lines of breaking waves, like a river flowing out to sea. The force of the current in a rip is strongest and fastest next to the surface of the water. Swimmers caught in a rip current and unaware of what is happening may exhaust themselves attempting to swim against the current. Rip currents are one of the leading causes of rescues by lifeguards and result in deaths every year.