The Sargasso Sea is the only sea named in the International Hydrographic Organization’s list that has no coastline.
Instead of being enclosed by land, the Sargasso Sea is defined by ocean currents in the North Atlantic. The North Atlantic Current, Gulf Stream, North Atlantic Equatorial Current, and Canary Current broadly form its boundaries. Its location and exact extent can shift because those currents vary.
The sea is famous for floating mats of Sargassum, a brown seaweed that can live and reproduce on the open ocean. Portuguese sailors noticed the seaweed during the Age of Discovery, and the region’s calm appearance helped inspire legends about ships becoming trapped there.
The Sargasso Sea is also important biologically. European and American eels migrate to the region to spawn, although the details of their life cycle have long challenged scientists. The sea should not be confused with the Sargassum-heavy waters that periodically wash onto Caribbean and Atlantic beaches.