(Latin, Oxus; Arabic, Jaihun), a river in the USSR, the largest in Middle Asia, lying partly on the border between the USSR and Afghanistan. It is formed by the confluence of the Piandzh (Panj) and the Vakhsh and discharges into the Aral Sea. Its length is 1,415 km or 2,540 km if measured from the source of the Piandzh. The area of the Amu Darya basin, as far as the city of Kerki, is 309,000 sq km, not counting the basins of the Zeravshan and the Kashkadar’ia. The catchment area which produces the volume of flow is 227,000 sq km (including the water basins of the Zeravshan and Kashkadar’ia rivers). The basic volume of flow of the Amu Darya derives from the water basins of the Piandzh and the Vakhsh, where névés and glaciers cover large areas (about 10,000 sq km). From the Piandzh-Vakhsh confluence to the Il’chik Gorge, the width of the present-day Amu Darya valley is usually 4–25 km. After passing through the Il’chik Gorge, the river valley becomes box shaped. It is considerably narrower than in the preceding region (for the most part no wider than 2–4 km). The Karakum and Kyzylkum deserts border directly on the river valley. Beyond the Tiuiamuiun Gorge, the Amu Darya passes through the alluvial deposits of an ancient delta; here the valley broadens, achieving a width of several dozen kilometers. The present-day delta begins at the village of Takhiiatos. The channel is subject to frequent variations; the river strays about over its floodplain, eroding now the left, now the right bank. Tributaries enter the Amu Darya only during the first 180 km; for the rest of its length the waters of the Amu Darya are tapped for irrigation and lost to evaporation and seepage, so that its flow gradually diminishes. The principal tributaries of the Amu Darya are the Surkhab (Kunduz), the Kafirnigan, and the Sur-khandar’ia. The water of the Amu Darya is derived mainly from the Piandzh and the Vakhsh, which are fed by glaciers and snow. Influx of water into the Amu Darya usually increases in March, as a result of the thawing of snow in the lower parts of its water basin and partly as a result of flooding from rains. Because of the thawing of snow, firns, and glaciers, the water of the Amu Darya is highest from June through August. Peak flow at the city of Kerki is usually reached in July; the low-water mark for the year is reached during January or February, only rarely in March. Up to 1960, the average volume of flow at Kerki was 2,000 cubic meters per second or 63 cubic kilometers a year. Because of increased tapping of water by the Karakum, Amu-Bukhar, and other canals, the volume of flow of the Amu Darya is diminishing, especially in the lower course of the river during the low-water period. The water of the Amu Darya is noted for its high turbidity (3.3 kilograms per cubic meter); the river has one of the highest figures of suspended sediment in the world. Up to 1960, the Amu Darya carried 210 million tons of sediment a year (at Kerki). The lower course of the Amu Darya freezes over every year. Near the city of Nukus, the river is icebound for almost four months. Along the river, especially the lower course, the banks are lined with tugaic forests (thickets of poplar, tamarisk, oleaster, and reeds). The Amu Darya is inhabited by various species of fish: Pseudoscaphirhynchus, sturgeon (Acipenser nudiventris), barbel, Aspius aspius, carp, and others.

The Amu Darya and its tributaries are important sources of irrigation water, supplying the Tadzhik, Uzbek, and Turkmen SSR’s, as well as Afghanistan. Not counting the basins of the Zeravshan and the Kashkadar’ia or Afghanistan, the Amu Darya basin has 1.26 million hectares of irrigated farmland. Owing to the closed character of the Aral Sea basin and its extremely unfavorable navigational conditions, the Amu Darya is of little value for transportation. The hydroelectric resources of the river and its tributaries are scant. The cities of Kerki and Chardzhou are located along the Amu Darya, and the cities of Urgench, Nukus, and Termez are near the river.

The Amu Darya, within whose basin were located the ancient states of Middle Asia—Chorasmia (at the mouth of the river), Sogdiana, and Bactria (on the middle and upper courses), was already well known in ancient times. In the Middle Ages and subsequently, the river functioned as a trade route from Rus’ to Chorasmia and Bukhara, by way of Astrakhan’ and Emba and then the Aral Sea. The Amu Darya has attracted great attention since the time of Peter I, who sought to bring the river into the orbit of Russian trade. It was at this time that Russian maps appeared, showing the Amu Darya as discharging into the Aral Sea. More or less systematic study of the river began only toward the end of the 19th or the start of the 20th century.