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(ôp), river, c.2,300 mi (3,700 km) long, W Siberian Russia. With the Irtysh River, its chief tributary, it is c.3,460 mi (5,600 km) long and is the world's fourth longest river. Formed by the junction of the Biya and Katun rivers (both of which rise in the Altai range) SW of Biysk, the upper Ob flows NW, then NE past Barnaul and Novosibirsk through the W Siberian lowlands to be joined by the Tom River. The middle Ob flows northwest through the swampy forests in the Tomsk and Narym regions and then is joined by the Chulym, Ket, and Irtysh rivers. The lower Ob consists of the Great Ob and the Small Ob and flows N, then E into Ob Bay, an estuary and shallow arm (c.500 mi/800 km long and 35–50 mi/56–80 km wide) of the Arctic Ocean between the Yamal and Gyda peninsulas. The width of the Ob increases downstream to c.25 mi (40 km) near its mouth. The valley of the middle Ob is subject to flooding each spring as the thaw occurs in the upper Ob basin before the ice in the lower course of the Ob has melted. Although frozen from five to six months of the year, the Ob is an important trade and transport route; Novosibirsk, Barnaul, Kamen-na-Obi, and Mogochin are the chief ports. There is a large hydroelectric power station at Novosibirsk. The largest oil and gas deposits in Russia are found in the basin of the middle and lower Ob. Severe pollution in the lower Ob has damaged the river's formerly famous fisheries.



a city (until 1969, settlement) in Novosibirsk Oblast, RSFSR. It has a railroad station 18 km west of Novosibirsk. Population, 23,000 in 1974. The chief industry is a plant producing sanitary-engineering equipment.



one of the great rivers in the USSR and the world; the third largest river in the Soviet Union, after the Enisei and the Lena, in terms of water volume. The Ob’ is formed by the confluence of the Biia and Katun’ rivers in the Altai, crosses Western Siberia from south to north, and empties into the Ob’ Bay of the Kara Sea. The Ob’ proper is 3,650 km long (from the source of the Irtysh, 5,410 km) and drains an area of 2,990 sq km (including drainless areas, 528,000 sq km). About 85 percent of the basin lies within the Western Siberian Plain. Its southeastern part is in the mountains of Southern Siberia—the Altai, Kuznetskii Alatau, Salair Ridge, and Gornaia Shoriia. There are more than 150,000 rivers in the basin. The basin’s physical geography ranges from semidesert in the south to tundra in the north, and much of its area is covered by forests and swamps.

In terms of river system, feeding, and regime, the Ob’ is divided into three sections: the upper Ob’ (to the mouth of the Tom’), the middle Ob’ (to the mouth of the Irtysh), and the lower Ob’ (to Ob’ Bay).

The upper part of the basin lies in mountains. Here rise the headwaters of the Ob’—the Biia and the Katun’—and many tributaries. The principal left tributaries are the Peschanaia, Anui, Charysh, and Alei, and the main right tributaries are the Chumysh and Inia. In its upper course the Ob’ has a well-developed valley with floodplain terraces. To the mouth of the Charysh it flows between low banks, and its bed has numerous channels, islands, and shoals. As it approaches Barnaul, its valley and floodplain become wider. From Barnaul to Kamen’-na-Obi the valley is broad (5–10 km) and asymmetric, with a steep left slope, and the wide floodplain is dissected by channels and lakes, including oxbow lakes. At Kamen’-na-Obi the valley and floodplain narrow to 3–5 km and 1.5–2 km, respectively, and outcrops of rock are encountered in the riverbed. In the southern part of Novosibirsk the river is blocked by a dam, forming the Novosibirsk Reservoir, also known as the Ob’ Sea. Below Novosibirsk the valley widens considerably, reaching 20 km at the mouth of the Tom’. During the low-water period the depth of the Ob’ fluctuates between 2 m and 6 m in its upper course, falling to 0.6 m in places in the shoals.

Below the mouth of the Tom’, where the middle Ob’ begins, and particularly below the Chulym, the Ob’ becomes a large deep river, and until its merger with the Irtysh it flows through taiga. Here the Ob’ Valley is 30–50 km wide, and the floodplain of 20–30 km is dissected by a dense network of channels. During low water, the river’s depth ranges from 4 m to 8 m. In its middle course the Ob’ receives, from the right, the Tom’, Chulym, Kef, Tym, Vakh, Trom”egan, Liamin, and Nazym and, from the left, the Shegarka, Chaia, Parabel’, Vasiugan, Bol’shoi Iugan, Bol’-shoi Salym, and the Irtysh.

After receiving the Irtysh, the Ob’ turns northward. Its valley is wide, in places exceeding 50 km, and asymmetrical, with a gently sloping and generally low left bank and a steep, precipitous right bank. The valley narrows to 4–8 km near Peregrebnoe and Salekhard. The vast floodplain, mainly on the left bank, is dissected by branches, channels, and lakes. During high-water periods the floodplain is inundated for up to 40–50 km. From the mouth of the Irtysh to Peregrebnoe the Ob’ flows in one channel with a depth of not less than 4–4.5 m. Below Peregrebnoe it divides into the Bol’shaia (Greater) and Malaia (Lesser) Ob’, with depths of 2.5–3 m during low water; after the two rivers merge the channel is more than 10 m deep. In the lower course the principal right tributaries are the Kazym and Polui, and the chief left tributaries are the Severnaia Sos’va and Shchuch’ia.

Before entering Ob’ Bay the river forms a delta covering more than 4,000 sq km. The main branches are the Khamanel’skaia Ob’ (left) and the larger Nadymskaia Ob’ (right), and beyond their mouths are the Iamsal’skii and Nadymskii bars. The average gradient of the Ob’ from Biisk to the Iamsal’skii bar is 0.054 m per km.

The Ob’ is fed chiefly by snow. During the spring and summer high water, the river carries most of its annual runoff. In the upper course high water begins in early April; in the middle course, in the second half of April; and in the lower course, in late April or early May. The water level begins to rise during the freeze-up, and when the river breaks up, there are brief rises in the water level caused by ice blocking. In the upper course high water ends in July; summer low water is unstable; and rain floods occur in September and October. In the middle and lower courses the abatement of high water, accompanied by rain floods, continues until the river freezes. The average fluctuation of the water level is 5 m in the upper course, increasing downstream to 9 m near Aleksandrovskoe. Before the confluence of the Ob’ and the Irtysh the fluctuation of the water level averages 7 m; below the influx of the Irtysh it reaches 10 m; and at the mouth it decreases to 5 m. The average discharge increases from 1,470 cu m per sec at Barnaul to 12,300 cu m per sec at Salekhard; the maximum discharge is 9,690 cu m per sec and 42,800 cu m per sec, respectively. The river is frozen over for 150 days in its upper course and 220 days in its lower course. In July the water temperature reaches 28°C along the Barnaul-Belogor’e stretch and 23°C in the lower reaches. The water mineralization is less than 200 mg per liter; only in the section between Novosibirsk and the mouth of the Tom’ does it exceed 200 mg per liter. The waters of the Ob’ contain much organic material and have a low oxygen level, causing fishkill. The average turbidity decreases downstream from 160 to 40 g per cu m. About 16 million tons of suspended sediment and a total of 50 million tons of solid matter are carried by the river annually.

The Ob’ basin has various natural resources. Western Siberia contains the USSR’s largest estimated reserves of petroleum, natural gas, and coal and half of the country’s peat reserves. The basin is also rich in water, forest, and other resources. About 50 fish species and subspecies are found in the Ob’ and Ob’ Bay, half of them of commercial importance. The most valuable species are sturgeon, sterlet, nelma, muksun, broad whitefish, whitefish, and peled, and the most common commercial fish are pike, ide, burbot, dace, roach, porgy, and perch.

The basin’s potential hydroelectric resources are estimated at 250 billion kW-hr. Three hydroelectric power plants are in operation—the Novosibirsk on the Ob’ and the Bukhtarma and Ust’-Kamenogorsk on the Irtysh. The Ob’ is the chief transportation artery of Western Siberia. It is navigable throughout its entire length, for 190 days in the upper course and 150 days in the lower reaches. The Ob’ and its tributaries have become increasingly important as waterways since the development of the region’s gas and oil deposits in the early 1960’s. The main ports and landings in the basin are Novosibirsk, Tomsk, Surgut, Labytnangi, Pavlodar, Omsk, Tobol’sk, and Tiumen’.


Zapadnaia Sibir’. Moscow, 1963. (Natural features and resources of the USSR.)
Ioganzen B. G. “Rybokhoziastvennye vodoemy Zapadnoi Sibiri i ikh biologo-promyslovaia kharakteristika.” Tr. Tomskogo gos. un-ta: Ser. biologicheskaia, 1953, vol. 125.
Cherniaeva, F. A. “Morfometricheskaia kharakteristika vodosbornykh basseinov sovetskikh arkticheskikh morei i vpadaiushchikh v nikh rek.” Gidrologiia rek Sovetskoi Arktiki Leningrad, 1965.
Resursy poverkhnostnykh vod SSSR, vol. 15, issue 2. Leningrad, 1972.
Domanitskii, A. P., R. G. Dubrovina, and A. I. Isaeva. Reki i ozera Sovetskogo Soiuza. Leningrad, 1971.




a Soviet diesel-electric ship. Built in the Netherlands in 1954; refitted in the USSR in 1955 for use on expeditions. Length, 130 m; width, 18 m; displacement, 12,600 tons. The Ob’ has scientific laboratories for hydrological, meteorological, geophysical, hydrochemical, and biological research. Since 1955 it has been conducting research in the arctic and antarctic. It participates in Soviet antarctic expeditions.


On drawings, abbr. for “obscure.”


a river in N central Russia, formed at Bisk by the confluence of the Biya and Katun Rivers and flowing generally north to the Gulf of Ob (an inlet of the Arctic Ocean): one of the largest rivers in the world, with a drainage basin of about 2 930 000 sq. km (1 131 000 sq. miles). Length: 3682 km (2287 miles)