Concept
is a bay located in the southern Kantō region of Japan, and spans the coasts of Tokyo, Kanagawa Prefecture, and Chiba Prefecture. Tokyo Bay is connected to the Pacific Ocean by the Uraga Channel. The Tokyo Bay region is both the most populous and largest industrialized area in Japan. In ancient times, Japanese knew Tokyo Bay as the 内海. By the Azuchi–Momoyama period (1568–1600) the area had become known as Edo Bay after the city of Edo. The bay took its present name in modern times, after the Imperial court moved to Edo and renamed the city Tokyo in 1868. Tokyo Bay juts prominently into the Kantō Plain. It is surrounded by the Bōsō Peninsula in Chiba Prefecture to the east and the Miura Peninsula in Kanagawa Prefecture to the west. The shore of Tokyo Bay consists of a diluvial plateau and is subject to rapid marine erosion. Sediments on the shore of the bay make for a smooth, continuous shoreline. In a narrow sense, Tokyo Bay is the area north of the straight line from Cape Kannon on the west of Miura Peninsula to Cape Futtsu on the east Bōsō Peninsula. This area covers about in 2012, reclamation projects continue to slowly shrink the bay. In a broader sense, Tokyo Bay includes the Uraga Channel. By this definition the bay opens from an area north of the straight line from Cape Tsurugisaki on the east of Miura Peninsula to Cape Sunosaki on the west of the Boso Peninsula. This area covers about . The area of Tokyo Bay combined with the Uraga Channel covers . The shoal between Cape Futtsu in Chiba Prefecture and Cape Honmaku in Yokohama is known as Nakanose, and has a depth of . North of this area the bay has a depth of and an uncomplicated underwater topography. Areas south of Nakanose are significantly deeper moving towards the Pacific Ocean. The only natural island in Tokyo Bay is Sarushima () at Yokosuka, Kanagawa Prefecture. Sarushima was one of the locations fortified with coastal artillery during the Bakumatsu period and was subsequently incorporated into the Tokyo Bay Fortress during the Meiji period.
