The is a

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of ...

Kanagawa is a prefecture of Japan located in the Kantō region of Honshu. Kanagawa Prefecture is the second-most populous prefecture of Japan at 9,221,129 (1 April 2022) and third-densest at . Its geographic area of makes it fifth-smallest. Kanagaw ...

and Yamanashi Prefectures on the island of

Honshū , historically called , is the largest and most populous island of Japan. It is located south of Hokkaidō across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyūshū across the Kanmon Straits. The island sepa ...

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...

. The upper reaches of the river in Yamanashi prefecture are also sometimes known as the , and the portion near the river mouth as the . The river overall was sometimes referred to as the from the

sweetfish Ayu or AYU may refer to: * Ayu (given name) * Ayu sweetfish (''Plecoglossus altivelis''), a species of smelt * ''Ayu'', a local name for the African manatee * Ayu (singer) or Ayumi Hamasaki, Japanese singer * Ayu Islands, a small archipelago in I ...

(''ayu'') which were once abundant in its waters. The Sagami River drains Lake Yamanaka, the largest and easternmost of the Fuji Five Lakes in Yamanashi Prefecture. It loops northwest, then northeast through Yamanashi, before following a generally southerly course to exit into

Sagami Bay 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 th ...

of the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the conti ...

between the cities of Hiratsuka and Chigasaki. It is dammed at several locations along the way, forming a number of reservoir lakes, the largest of which are Lake Sagami and Lake Tsukui. The river has had to re-cut its course several times due to repeated eruptions of

Mount Fuji , or Fugaku, located on the island of Honshū, is the highest mountain in Japan, with a summit elevation of . It is the second-highest volcano located on an island in Asia (after Mount Kerinci on the island of Sumatra), and seventh-highest ...

, and

river terrace Fluvial terraces are elongated terraces that flank the sides of floodplains and fluvial valleys all over the world. They consist of a relatively level strip of land, called a "tread", separated from either an adjacent floodplain, other fluvial te ...

s are in evidence along its upper reaches in Yamanashi. As the river crosses Kanagawa, it forms natural

levees A levee (), dike (American English), dyke (Commonwealth English), embankment, floodbank, or stop bank is a structure that is usually earthen and that often runs parallel to the course of a river in its floodplain or along low-lying coastli ...

in the soft soils of the

alluvial plain An alluvial plain is a largely flat landform created by the deposition of sediment over a long period of time by one or more rivers coming from highland regions, from which alluvial soil forms. A floodplain is part of the process, being the smal ...

s of central Kanagawa's

Sagamino plateau The , also known as the or , is a wide plateau situated between the Tama Hills and the Sagami River in Kanagawa Prefecture, Japan. Near its northern boundary with the city of Sagamihara is a city in Kanagawa Prefecture, Japan. , the city ...

, and forms almost no

river delta A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more rare ...

as it exits into the ocean. The potential of the upper reaches of the Sagami River for hydroelectric power development began to be developed in the 1930s, with the growth of industry and electrical consumption in the

Yokohama is the second-largest city in Japan by population and the most populous municipality of Japan. It is the capital city and the most populous city in Kanagawa Prefecture, with a 2020 population of 3.8 million. It lies on Tokyo Bay, south of T ...

industrial belt, and the growing need for a reliable supply of drinking and industrial water. Work on the Sagami Dam began in 1938; however, lack of funding and the advent of

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...

delayed completion until after the end of the war. In the post war period, the

Shiroyama Dam The is a multi-purpose dam on the main stream Sagami River in Sagamihara, Kanagawa Prefecture on the island of Honshū, Japan. History The potential of the Sagami River valley for hydroelectric power development began to be developed in the ...

was also completed on the main stream of the Sagami River in 1965. A number of dams have also been completed on the Nakatsu River, the main

tributary A tributary, or affluent, is a stream or river that flows into a larger stream or main stem (or parent) river or a lake. A tributary does not flow directly into a sea or ocean. Tributaries and the main stem river drain the surrounding drai ...

of the Sagami River, including the

Miyagase Dam The is a dam on the Nakatsu River, a main tributary of the Sagami River in Aikō District, Kanagawa Prefecture, Japan. It straddles the border between the village of Kiyokawa, town of Aikawa and the former town of Tsukui (now part of the ...

External links

Sagami River Science Museum, Sagamihara
(mouth) {{Authority control Rivers of Kanagawa Prefecture Rivers of Yamanashi Prefecture Rivers of Japan