The region (actually in the horse latitudes) of the North Atlantic Ocean to the east and south of the Gulf Stream system. This is a region of convergence of the surface waters, and is characterized by clear, warm water, a deep blue color, and large quantities of floating sargassum or "gulf weed."

The Sargasso Sea is an elongated region in the middle of the North Atlantic Ocean, surrounded by ocean currents. On the west it is bounded by the Gulf Stream; on the north, it is bounded by the North Atlantic Current; on the east, it is bounded by the Canary Current; and on the south, it is bounded by the North Atlantic Equatorial Current. It is, very roughly, 700 statute miles wide and 2,000 statute miles long (1,100 km wide and 3,200 km long).