This image provided by NOAA, pictures a harmless green dye used to show a rip current. Rip currents are powerful, narrow channels of fast-moving water that are prevalent along the East, Gulf, and West coasts of the U.S., as well as along the shores of the Great Lakes. About 100 people drown from rip currents along U.S. beaches each year, according to the U.S. Lifesaving Association. (NOAA via AP)