The Denmark Strait's "underwater waterfall"

In the Denmark Strait between Greenland and Iceland, cold, dense water from the Nordic Seas flows over a submerged ridge and sinks beneath warmer water from the Irminger Sea. This deep current is often called an underwater waterfall: it begins at roughly 650 m and descends along the seabed to around 3,000 m. NOAA estimates its transport at about 3.5 million cubic metres per second—a calculated flow, not a visible wall of water from the surface.