is a river in Hokkaidō

Hokkaido

, formerly known as Ezo, Yezo, Yeso, or Yesso, is Japan's second largest island; it is also the largest and northernmost of Japan's 47 prefectural-level subdivisions. The Tsugaru Strait separates Hokkaido from Honshu, although the two islands are connected by the underwater railway Seikan Tunnel...

, Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

. At 268 kilometres (166.5 mi) in length, the river is the third longest in Japan and the longest in Hokkaidō. The river has a drainage area of 14330 square kilometre, making it the second largest in Japan, as is its total discharge of around 14.8 cubic kilometres (3.6 cu mi) per year.

It rises from Mount Ishikari

Mount Ishikari

is part of the Ishikari Mountains, Hokkaidō, Japan. On its slopes are the head waters of the Ishikari River.- References :* , Seamless Digital Geographical Map of Japan, Geological Survey of Japan, AIST . 2007....

 and flows through Asahikawa

Asahikawa, Hokkaido

is a city in Kamikawa Subprefecture, Hokkaido, Japan. It is the capital of the subprefecture and the second-largest city in Hokkaido, after Sapporo. It has been a Core city since April 1, 2000...

 and Sapporo. Major tributaries of the river include Chūbetsu, Uryū, Sorachi and Toyohira

Toyohira River

The Toyohira River is a river in Hokkaidō prefecture, Japan. It is 72.5km in length and has drainage area of 959km². It is a tributary of the Ishikari River....

. Until 40,000 years ago, it fell into the Pacific Ocean

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

 near Tomakomai

Tomakomai, Hokkaido

is a city and port located in Iburi, Hokkaido, Japan. Though its name implies a small, idyllic town, it is the largest city in the Iburi Subprefecture. As of 2008, it had an estimated population of 173,504 and a population density of 310 persons per km²...

. Lava

Lava

Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...

 from the volcanic Shikotsu mountains dammed up the river and moved its mouth to the Sea of Japan

Sea of Japan

The Sea of Japan is a marginal sea of the western Pacific Ocean, between the Asian mainland, the Japanese archipelago and Sakhalin. It is bordered by Japan, North Korea, Russia and South Korea. Like the Mediterranean Sea, it has almost no tides due to its nearly complete enclosure from the Pacific...

.

The name of the river is derived from the Ainu

Ainu language

Ainu is one of the Ainu languages, spoken by members of the Ainu ethnic group on the northern Japanese island of Hokkaidō....

 word winding river. As it suggests, the river once meandered in the Ishikari plain and was as long as the Shinano River

Shinano River

The Shinano River is the longest and largest river in Japan. It flows from Nagano Prefecture to Niigata Prefecture. It is called the Chikuma River in Nagano Prefecture....

, the longest river in Japan. Massive construction shortened the river by 100 kilometers and left many in the plain.