When you look underwater, what is making the seagrass wave in the water? The answer is ocean currents. Ocean currents are continuous movements of water in the ocean that follow set paths, kind of like rivers in the ocean. They can be at the water's surface or go to the deep sea; some are very large, like Japan's Kuroshio Current, which is equal in volume to 6,000 large rivers, while others are small and unnamed. They can be caused by tides, wind or thermohaline (heat and salt) circulation. To learn more about what puts the motion in the ocean, watch this video from NOAA's National Ocean Service. (Read the video's transcript here.)