What is the only sea without a land coastline?

The Sargasso Sea is the only sea without a land coastline. Instead of being enclosed by shores, it is defined by ocean currents in the North Atlantic: the Gulf Stream, North Atlantic Current, Canary Current, and North Atlantic Equatorial Current.

The sea is named for Sargassum, a floating brown seaweed that forms large mats at the surface. Christopher Columbus reported seeing substantial quantities of floating seaweed in the region during his Atlantic voyages. The relatively calm, circular current system known as the North Atlantic gyre allows the seaweed to accumulate.

The Sargasso Sea has no universally fixed boundary because its edges are described by changing currents rather than permanent landforms. It is an important habitat for species such as the European eel and American eel, which travel to the region to reproduce. The Bermuda region lies within the broader Sargasso Sea, but Bermuda does not define the sea’s boundary.