What is the name of the world's largest underwater waterfall?

The world’s largest known underwater waterfall is the Denmark Strait cataract. It occurs in the Denmark Strait between Greenland and Iceland, where dense, cold water from the Nordic seas spills southward over an underwater ridge.

This phenomenon is better described scientifically as an undersea overflow than as a waterfall. Because cold, salty water is denser than the warmer water below it, gravity pulls the flow down along the seafloor. The descent reaches roughly 3.5 kilometers, making it taller than Angel Falls, the highest uninterrupted waterfall on land.

The cataract is also enormous in volume, transporting about 3.2 million cubic meters of water per second. That dense water becomes part of North Atlantic Deep Water, an important component of the Atlantic overturning circulation. Its location is the Denmark Strait, but the cataract itself is an underwater current and cascade rather than a visible vertical drop like Niagara Falls.