Earth's biggest waterfall is completely underwater

Between Greenland and Iceland, cold water from the Nordic Seas sinks beneath warmer Atlantic water and plunges roughly 3,500 metres — several times taller than any waterfall on land. The submarine cataract moves an estimated 3.5 million cubic metres of water per second, yet it's entirely invisible from the surface.

— NOAA National Ocean Service, Where is Earth's Largest Waterfall? — NOAA Ocean Facts