Japan’s Inland Sea stitches three main islands together
The Seto Inland Sea separates Honshu, Shikoku, and Kyushu while linking the Pacific to the Sea of Japan and feeding Osaka Bay’s industrial ports. Eleven prefectures touch its shores, including Hiroshima, Takamatsu, and Matsuyama along the warmer, drier Setouchi coast.
The sea stretches about 450 kilometres from east to west and between 15 and 55 kilometres from north to south. Most of it is shallow, averaging 38 metres with a deepest point of 105. Despite the name, hydrologists class it as a marginal sea of the Pacific, partly enclosed by Japan’s main islands, rather than a true inland body like the Caspian.
Several openings connect it to the wider ocean. In the east the Naruto Strait leads to the Kii Channel and the Pacific; in the west the Kanmon Straits reach the Sea of Japan and the Bungo Channel opens south to the Pacific. The International Hydrographic Organization’s 1953 limits use Shimonoseki in the west, the Kii Channel via Awaji in the east, and a line from Sada Misaki on Shikoku to Seki Saki on Kyushu in the south.
Individual stretches carry their own names, such as Iyo-nada between Ehime, Yamaguchi and Ōita, Aki-nada west of the Geiyo Islands near Hiroshima, and Suō-nada off Yamaguchi. Nearly 3,000 islands are scattered across it, many uninhabited. Awaji is the largest and Shōdo the second, followed by clusters such as the Naoshima and Shiwaku islands in the east, the Geiyo group and Itsukushima, better known as Miyajima, in the centre, and Suō-Ōshima in the west.
Its shores enjoy a warm climate with relatively little rain, the Setouchi weather that shapes coastal life. Dense blooms of phytoplankton cause periodic red tides that kill fish, and since the 1980s the northern and southern corridors have come under growing environmental strain while ships keep crowding the passage.
Source: Seto Inland Sea
