Sagami Bay (相模湾, also known as the Sagami Gulf or Sagami Sea) lies south of Kanagawa Prefecture in Honshu, central Japan, contained within the scope of the Miura Peninsula, in Kanagawa, to the east, the Izu Peninsula, in Shizuoka Prefecture, to the west, and the Shōnan coastline to the north, while the island of Izu Ōshima marks the southern extent of the bay. It lies approximately 40 kilometres (25 miles) southwest of Tokyo.
 Natural environment
A branch of the warm Kuroshio Current warms the bay, allowing it to host marine organisms typical of more southerly regions and giving a mild climate to the land bordering it. The maximum depth of Sagami Bay is about 1500 meters.
Organisms from sub-arctic regions are advected into the bay by intrusions of the Oyashio Current resulting in very high biodiversity. It is the major study site for research programs at the University of Tokyo (ORI) and the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). In 2004, soil samples from Sagami Bay were found to contain radioactive contamination from the Bikini Atoll nuclear tests that took place from 1946 to 1958.