is a lake in Abashiri

Abashiri, Hokkaido

is a city located in Okhotsk Subprefecture, Hokkaido, Japan.Abashiri is known as the site of the Abashiri Prison, a Meiji-era facility used for the incarceration of political prisoners...

, 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...

. It is located in Abashiri Quasi-National Park

Abashiri Quasi-National Park

is a quasi-national park in Japan. The park protects the waters and surrounding coastline of the lakes and lagoons along the Sea of Okhotsk on Hokkaidō. This includes such lakes as Lake Abashiri and Lake Notoro as well as Lake Tōfutsu and Lake Saroma. Lake Saroma is the fourth largest lake in Japan...

. The Abashiri

Abashiri River

is a river in Hokkaidō, Japan.-History:Around 1000 years ago, the Okhotsk culture settled the river basin and moved inland. Remains from the Jōmon period have been found on the bottom of Lake Abashiri.-Course:...

 and Memanbetsu Rivers flow into the lake. Water exits the lake through the Abashiri River again and flows 7 kilometres (4.3 mi) to the Sea of Okhotsk

Sea of Okhotsk

The Sea of Okhotsk is a marginal sea of the western Pacific Ocean, lying between the Kamchatka Peninsula on the east, the Kuril Islands on the southeast, the island of Hokkaidō to the far south, the island of Sakhalin along the west, and a long stretch of eastern Siberian coast along the west and...

.

History and formation

From core samples taken from the lake bed, the lake basin appears to have first formed some 20,000 years ago during the last period of glaciation. During the last 6000 years, the Abashiri River carved out the lake bed. Artifacts from the Jōmon period

Jomon period

The is the time in Japanese prehistory from about 14,000 BC to 300 BC.The term jōmon means "cord-patterned" in Japanese. This refers to the pottery style characteristic of the Jōmon culture, and which has markings made using sticks with cords wrapped around them...

 have been found in the area around the Memanbetsu River. In modern times, the course of the Abashiri River has been straightened to provide for irrigation

Irrigation

Irrigation may be defined as the science of artificial application of water to the land or soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall...

 resulting in a serious siltation

Siltation

Siltation is the pollution of water by fine particulate terrestrial clastic material, with a particle size dominated by silt or clay. It refers both to the increased concentration of suspended sediments, and to the increased accumulation of fine sediments on bottoms where they are undesirable...

 problem for the lake.

Freezing and salinity

The lake freezes over from December to April with ice up to a meter thick. The reduced inflow of water during the winter season causes saltwater to flow upstream from the Sea of Okhotsk

Sea of Okhotsk

The Sea of Okhotsk is a marginal sea of the western Pacific Ocean, lying between the Kamchatka Peninsula on the east, the Kuril Islands on the southeast, the island of Hokkaidō to the far south, the island of Sakhalin along the west, and a long stretch of eastern Siberian coast along the west and...

 and into the lake. This influx of saltwater has created a layer of water with 10,000 ppm of chlorine

Chlorine

Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

, 10 metres (32.8 ft) below the surface of the lake.

Fauna

Delta smelt

Delta smelt

Delta smelt, Hypomesus transpacificus, is an endangered slender-bodied smelt, about long, of the Osmeridae family. Endemic to the upper Sacramento-San Joaquin estuary of California, it mainly inhabits the freshwater-saltwater mixing zone of the estuary, except during its spawning season, which...

, chum salmon

Chum salmon

The chum salmon, Oncorhynchus keta, is a species of anadromous fish in the salmon family. It is a Pacific salmon, and may also be known as dog salmon or Keta salmon, and is often marketed under the name Silverbrite salmon...

 and cherry salmon are the most important sport-fish. In 1980, approximately 650 tons of fish were caught. Ice Goby (Leucopsarion petersi) can also be found in the lake.