Great river's

Purus

Purus (pOOrOOz') [key], river, c.2,100 mi (3,380 km) long, rising in the Andes Mts., E Peru. It flows generally northeast in a meandering course, across Acre and Amazonas states, NW Brazil, to the Amazon River. Mostly navigable, it traverses a rubber-producing region and receives the Acre River at Bôca do Acre.

The Purus is a river in South America. Its drainage basin is 63,166 km². The mean discharge is 8,400 m³/s.

It enters the Amazon River west of the Madeira River, which it parallels as far south as the falls of the latter stream. It runs through a continuous forest at the bottom of the great depression lying between the Madeira River, which skirts the edge of the Brazilian sandstone plateau, and the Ucayali which hugs the base of the Andes.

One of its marked features is the five parallel furos which from the north-west at almost regular intervals the Amazon sends to the Purus; the most south-westerly one being about 150 miles (240 km) above the mouth of the latter river. They cut a great area of very low-lying country into five islands. Farther down the Purfis to the right three smaller furos also connect it with the Amazon.

William Chandless found its elevation above sea-level to be only 107 feet (33 m) 590 miles (950 km) from its mouth. It is one of the most crooked streams in the world, and its length in a straight line is less than half that by its curves. It is practically only a drainage ditch for the half-submerged, lake-flooded district it traverses.

Its width is very uniform for 1000 miles (1600 km) up, and for 800 miles (1300 km) its depth is never less than 45 feet (15 m).

It is navigable by steamers for 1648 miles (2650 km) as far as the little stream, the Curumaha, but only by light-draft craft. Chandless ascended it 1866 miles (3,000 km). At 1792 miles (2,880 km) it forks into two small streams. Occasionally a cliff touches the river, but in general the lands are subject to yearly inundations throughout its course, the river rising at times above 50 feet (15 m), the numerous lakes to the right and left serving as reservoirs.

Its main tributary, the Aquiry or Acre River, enters from the right about 1104 miles (1777 km) from the Amazon. Its sources are near those of the Mayutata. It is navigable for a period of about five months of the year, when the Purus valley is inundated; and, for the remaining seven months, only canoes can ascend it sufficiently high to communicate overland with the settlements in the great india-rubber districts of the Mayutata and lower Beni; thus these regions are forced to seek a canoe outlet for their rich products by the very dangerous, costly and laborious route of the falls of the Madeira River.

Great river's

Madeira

Madeira (mudā'ru) [key], river, c.2,100 mi (3,380 km) long, formed by the junction of the Beni and Mamoré rivers on the Bolivia-Brazil border. It flows north along the border for c.60 mi (100 km), then northeast in a winding course through the Rondônia and Amazonas sections of NW Brazil into the Amazon River. At its mouth is Ilha Tupinambaranas, an extensive marshy region formed by the Madeira's distributaries. The river receives numerous tributaries from the southeast and is navigable by ocean vessels to the falls and rapids near Pôrto Velho, Brazil. There the Madeira-Mamoré RR begins a 227 mi (365 km) run around the unnavigable section to Guajará-Mirim on the Mamoré River.

The Madeira River is a major waterway in South America, approximately 3,380 km (2,100 miles) long. Madeira is the longest tributary of Amazon.

The mean inter-annual precipitations on the great basins vary from 750 to 3000 mm, the entire upper Madeira basin receiving 1705 mm/yr. The greatest extremes of rainfall are between 490 mm and more than 7000 mm. At its head, the Madeira on its own is still one of the largest rivers of the world, with a mean inter-annual discharge of 17,000 m³/s, i.e. 536 km³/yr, approximately half the discharge of the Congo River. The mean inter-annual contribution of the Bolivian Andes is 4170 m³/s, i.e. 132 km³/yr, representing 25% of the discharge of the entire upper Madeira basin.

Between Guajará-Mirim and the falls, the Madeira receives the drainage of the north-eastern slopes of the Andes from Santa Cruz de la Sierra to Cuzco, the whole of the south-western slope of Brazilian Mato Grosso and the northern slope of the Chiquitos sierras. In total, the catchment area is 850,000 km²,^[1] almost equal in area to France and Spain combined. The waters flow into the Madeira from many large rivers, the principal of which, (from east to west), are the Guaporé or Itenez, the Baures and Blanco, the Itonama or San Miguel, the Mamoré, Beni, and Mayutata or Madre de Dios, all of which are reinforced by numerous secondary but powerful affluents.

All of the upper branches of the river Madeira find their way to the falls across the open, almost level Mojos and Beni plains, 90,000 km² (35,000 square miles) of which are yearly flooded to an average depth of about 3 feet (0.91 m) for a period of from three to four months.

From the falls, the Madeira flows northward forming the border between Bolivia and Brazil for approximately 100 km (60 miles). Below the confluence of the Rio Abunã, the Madeira meanders north-eastward through the Rondônia and Amazonas states of north west Brazil to its junction with the Amazon. At its mouth is Ilha Tupinambaranas, an extensive marshy region formed by the Madeira’s distributaries.

It rises more than 15 m (50 ft) during the rainy season, and ocean vessels may ascend it to the Falls of San Antonio, near Porto Velho, Brazil, 1070 km (663 miles) above its mouth; but in the dry months, from June to November, it is only navigable for the same distance for craft drawing about 2 m (from 5 to 6 feet) of water. The Madeira-Mamoré Railroad runs in a 365 km (227 mile) loop around the unnavigable section to Guajará-Mirim on the Mamoré River.

A subspecies of Boto (Amazon River Dolphin) is known to inhabit the Madeira river system.

In July 2007, plans have been approved by the Brazilian Government to construct two hydroelectric dams on the Madeira River, and is opposed by certain groups such as environmentalists for the environmental impact that the construction could have.^[2]

Great river's

Volga

Volga (vol'gu, Rus. vôl'gu) [key], river, c.2,300 mi (3,700 km) long, central and E European Russia. It is the longest river of Europe and the principal waterway of Russia, being navigable (with locks bypassing the dams) almost throughout its course. Its basin forms about one third of European Russia. The Volga has played an important part in the life of the Russian people, and it is characteristically named in Russian folklore “Mother Volga.” For centuries it has served as the chief thoroughfare of Russia and as the lifeline of Russian colonization to the east. It carries one half of the total river freight of Russia and irrigates the vast steppes of the lower Volga region. Grain, building materials, salt, fish, and caviar (from the Volga delta and the Caspian Sea) are shipped upstream; lumber is the main commodity shipped downstream.

Rising at an altitude of only 742 ft (226 m) in the Valday Hills, it winds E past Rzhev and Tver, through the Rybinsk Reservoir, and past Shcherbakov, Yaroslavl, Kostroma, and Nizhny Novgorod (formerly Gorky) to Kazan, where it turns south and continues its broad, majestic course past Ulyanovsk, Samara, Saratov, and Volgograd. From Volgograd (c.300 mi/480 km upstream) the Volga River flows in a course below sea level through the Caspian lowland. The Volga enters the Caspian Sea through a wide delta below Astrakhan.

The Volga's chief tributaries are the Oka, Sura, Vetluga, Kama, and Samara rivers. The chief ports are Tver, Nizhny Novgorod, Kazan, Samara, Volgograd, Astrakhan, Saratov, Yaroslavl, and Rybinsk. The Volga-Baltic Waterway links the Volga with the Baltic Sea and with the Baltic–White Sea Canal; the Volga-Don Canal links the Volga with the Azov and Black Seas; the Moscow Canal connects it directly with Moscow.

In its upper course the Volga traverses numerous lakes. Below Nizhny Novgorod it broadens considerably and is lined on its right (western) bank by the bluffs of the Volga Hills, which contrast sharply with the steppe that extends from the left bank. The Zhiguli Mts. cause the river to make a sharp bend (the Samara Bend), which reaches its easternmost point at Samara. The Volga is navigable from late April to late November at Shcherbakov and from early March to mid-December at Astrakhan. A tranquil, regular stream, it has a flood stage in May and June and a low-water stage in the late summer, when shoals and sandbars impede navigation.

Great river's

Missouri

Missouri, river, c.2,565 mi (4,130 km) long (including its Jefferson-Beaverhead-Red Rock headstream), the longest river of the United States and the principal tributary of the Mississippi River. The length of the combined Missouri-Mississippi system from the headwaters of the Missouri to the mouth of the Mississippi is c.3,740 mi (6,020 km), making it the world's third longest river after the Nile and the Amazon. The Missouri River drains an area of c.580,000 sq mi (1,502,200 sq km), including 2,550 sq mi (6,600 sq km) in Canada.

Above Sioux City, Iowa, the Missouri's fluctuating flow is regulated by seven major dams (Gavins Point, Fort Randall, Big Bend, Oahe, Garrison, Fort Peck, and Canyon Ferry) and more than 80 other dams on tributary streams. These dams, with their reservoirs, are part of the coordinated, basin-wide Missouri River basin project (authorized by the U.S. Congress in 1944), which provides for flood control, hydroelectric power, irrigation water, and recreational facilities. The dams serve to impound for later use the spring rains and snowmelt that swell the volume of the river in March and April and also the second flood stage that frequently occurs in June as the snow melts in the remoter mountain regions. Despite this system of dams, during the extremely rainy summer of 1993 the lower Missouri reached record levels, flooding many areas, eroding farmland, and depositing huge quantities of sand that damaged many thousands of acres of fertile bottomland.

Since the dams have no locks, Sioux City is the head of navigation for the 9-ft (2.7-m) channel maintained over the 760-mi (1,223-km) stretch downstream to the Mississippi. Tugboats pushing strings of barges move freight along this route. From December to March, navigation is interrupted by ice and low water levels (resulting from upstream freezing); summer water levels, which frequently fell so low as to cause river boats to go aground, are now maintained at safe levels by the release of water from Gavin Point Dam. Silt, fertilizers, and pesticides, which are contained in the runoff from agricultural lands, pollute the water above Sioux City, but wastes from industrial plants and from inadequately treated municipal sewage create a more serious level of pollution downstream. There has been a reduction in wetland areas and a loss of fish and wildlife due to the damming of the river.

Great river's

Mississippi

Mississippi, river, principal river of the United States, c.2,350 mi (3,780 km) long, exceeded in length only by the Missouri River, the chief of its numerous tributaries. The combined Missouri-Mississippi system (from the Missouri's headwaters in the Rocky Mts. to the mouth of the Mississippi River) is c.3,740 mi (6,020 km) long and ranks as the world's third longest river system after the Nile and the Amazon. With its tributaries, the Mississippi drains c.1,231,000 sq mi (3,188,290 sq km) of the central United States, including all or part of 31 states and c.13,000 sq mi (33,670 sq km) of Alberta and Saskatchewan in Canada. Cotton and rice are important crops in the lower Mississippi valley; sugarcane is raised in the delta. The Mississippi is abundant in freshwater fish; shrimp are taken from the briny delta waters. The delta also yields sulfur, oil, and gas.

The Mississippi River rises in small streams that feed Lake Itasca (alt. 1,463 ft/446 m) in N Minnesota and flows generally south to enter the Gulf of Mexico through a huge delta in SE Louisiana. A major economic waterway, the river is navigable from the sediment-free channel maintained through South Pass in the delta to the Falls of St. Anthony in Minneapolis, with canals circumventing the rapids near Rock Island, Ill., and Keokuk, Iowa. For the low-water months of July, August, and September, there is a 45-ft (13.7-m) channel navigable by oceangoing vessels from Head of the Passes to Baton Rouge, La., and a 9-ft (2.7-m) channel from Baton Rouge deep enough for barges and towboats to Minneapolis. The Mississippi connects with the Intracoastal Waterway in the south and with the Great Lakes–St. Lawrence Seaway system in the north by way of the Illinois Waterway.

Along the river's upper course shipping is interrupted by ice from December to March; thick, hazardous fogs frequently settle on the cold waters of the unfrozen sections during warm spells from December to May. In its upper course the river is controlled by numerous dams and falls c.700 ft (210 m) in the 513-mi (826-km) stretch from Lake Itasca to Minneapolis and then falls c.490 ft (150 m) in 856 mi (1,378 km) from Minneapolis to Cairo, Ill. The Mississippi River receives the Missouri River 17 mi (27 km) N of St. Louis and expands to a width of c.3,500 ft (1,070 m); it swells to c.4,500 ft (1,370 m) at Cairo, where it receives the Ohio River.

The lower Mississippi meanders in great loops across a broad alluvial plain (25–125 mi/40–201 km wide) that stretches from Cape Girardeau, Mo., to the delta region S of Natchez, Miss. The plain is marked with oxbow lakes and marshes that are remnants of the river's former channels. Natural levees, built up from sediment carried and deposited in times of flood, border the river for much of its length; sediment has also been deposited on the riverbed, so that in places the surface of the Mississippi is above that of the surrounding plain, as evidenced by the St. Francis, Black, Yazoo, and Tensas river basins. Breaks in the levees frequently flood the fertile bottomlands of these and other low-lying areas of the plain.

After receiving the Arkansas and Red rivers, the Mississippi enters a birdsfoot-type delta, which was built outward by sediment carried by the main stream since c.A.D. 1500 It then discharges into the Gulf of Mexico through a number of distributaries, the most important being the Atchafalaya River and Bayou Lafourche. The main stream continues southeast through the delta to enter the gulf through several mouths, including Southeast Pass, South Pass, and Pass à Loutre. Indications that the Mississippi River might abandon this course and divert through the Atchafalaya River led to the construction of a series of dams, locks, and canals by the U.S. Army Corps of Engineers. Known as the Old River Control Structure, it was undertaken to prevent such an occurrence. Sluggish bayous and freshwater lakes (such as Pontchartrain, Grand, and Salvador) dot the delta region.

Regarding the delta, environmentalists and those in the seafood industry are concerned by the loss of 25–45 sq mi (65–104 sq km) of marsh a year; fish and wildlife populations are threatened as their natural habitat slowly disappears. The loss has been attributed to subsidence and a decrease in sediment largely due to dams, artificial channeling, and land conservation measures. Pollution and the cutting of new waterways for petroleum exploration and drilling have also taken their toll on the delta. Louisiana has enacted environmental protection laws that are expected to slow, but not halt, the loss of the delta marshes.

Great river's

Mekong

Mekong (mā'kong, mē'–) [key], Chinese Lancang, one of the great rivers of SE Asia, c.2,600 mi (4,180 km) long. From its marshy source (definitively identified in 1994) on the Rup-sa Pass in the highlands of Tibet, it rises as the Za Qu (Dza Chu) and flows generally S through Yunnan prov. in deep gorges and over rapids. Leaving Yunnan, the Mekong forms the Myanmar-Laos border, then curves E and S through NW Laos before marking part of the Laos-Thailand border.

From SW Laos the river descends onto the Cambodian plain, where it receives water from Tônlé Sap during the dry season by way of the Tônlé Sap River; during the rainy season, however, the floodwaters of the Mekong reverse the direction of the Tônlé Sap River and flow into Tônlé Sap, a lake that is a natural reservoir. The Mekong River finally flows into the South China Sea through many distributaries in the vast Mekong delta (c.75,000 sq mi/194,250 sq km), which occupies SE Cambodia and S Vietnam. The delta, crisscrossed by many channels and canals, is one of the greatest rice-growing areas of Asia. It is a densely populated region; Vinh Long, Can Tho, and Long Xuyen are the chief towns there. Ho Chi Minh City (Saigon) is located just east of the delta. The Mekong delta was the scene of heavy fighting in the Vietnam War.

The Mekong River is navigable for large vessels c.340 mi (550 km) upstream; Phnom Penh is a major port. North of the Cambodian border, the Mekong is navigable in short sections. At Khone Falls, a series of rapids (6 mi/9.7 km long) in S Laos, the Mekong drops 72 ft (22 m). The falls are the site of a hydroelectric power station, part of the Mekong Scheme, a project undertaken by the United Nations in the early 1960s to develop the potentials of the lower Mekong basin. The project sought to improve navigation, provide irrigation facilities, and produce hydroelectricity. The Mekong River Commission, whose members consist of Cambodia, Thailand, Laos, and Vietnam, intends to pursue similar joint projects and to explore the establishment of fisheries and the construction of a trans-Indochinese roadway system. China is developing the upper Mekong, constructing a series of dams to provide hydroelectric power and a navigable waterway; the first, at Manwan, was completed in 1993.

Great River's

Niger

Niger (nī'jur) [key], great river of W Africa, c.2,600 mi (4,180 km) long, rising on the Fouta Djallon plateau, SW Guinea, and flowing NE through Guinea and into Mali. In central Mali the Niger forms its vast inland delta (c.30,000 sq mi/77,700 sq km), a maze of channels and shallow lakes. An irrigation project in the delta, begun by the French in the 1930s and including a large dam at Sansanding (1941), has opened more than 100,000 acres (40,470 hectares) to farming, especially rice cultivation. Downstream from Timbuktu, Mali, the Niger begins a great bend, flowing first E and then SE out of Mali, through the Republic of Niger (where it forms part of the border with Benin), and into Nigeria; the river also becomes increasingly polluted.

At Lokoja, central Nigeria, the Benue, its chief tributary, joins the Niger, which then flows south, emptying through a great delta into the Gulf of Guinea. The delta (c.14,000 sq mi/36,260 sq km)—the largest in Africa—is characterized by swamps, lagoons, and navigable channels. The region is a major source of palm oil and petroleum. Major towns in the delta are Port Harcourt and Bonny. Much of the Niger is seasonally navigable, and below Lokoja it is open to ships virtually all year. The Niger is a major source of fish, especially perch and tiger fish. A hydroelectric and irrigation project, centered around the Kainji dam (1968), is located on the Niger near Jebba, Nigeria.

The upper Niger region was an important part of the former empires of Mali and Songhai. The course of the Niger long puzzled European geographers; only from 1795 to 1797 did Mungo Park, the Scots explorer, correctly establish the eastern flow of the upper Niger, and it was not until 1830 that Richard and John Lander, English explorers, found that the river emptied into the Gulf of Guinea.

Benin, Burkina Faso, Cameroon, Chad, Côte d'Ivoire, Guinea, Mali, Niger, and Nigeria are members of the Niger Basin Authority, which was founded in 1960 and given its present name in 1984. It promotes the cooperative development and management of the Niger River and its basin. The water level of the Niger has been substantially lowered as a result of the long-term W African drought in the late 1960s, 70s, and 80s; in 1985 and 1990 sections of the river dried up.

Great River's

Mackenzie

Mackenzie, river, c.1,120 mi (1,800 km) long, issuing from Great Slave Lake, Northwest Territories, Canada, and flowing generally NW to the Arctic Ocean through a great delta. Between Great Slave Lake and Lake Athabasca it is known as the Slave River. At Lake Athabasca, the Finlay-Peace river system and the Athabasca River join the Mackenzie. The Finlay-Peace-Mackenzie system (c.2,600 mi/4,180 km long) is the second longest continuous stream in North America. The Liard River is the largest tributary flowing directly into the Mackenzie. The river is navigable from the Arctic Ocean to Great Slave Lake between June and October. Between Great Slave Lake and Lake Athabasca there are rapids (14 mi/23 km) that must be portaged; above the rapids are more than 400 mi (644 km) of navigable waters. The Liard River affords transportation between Fort Nelson, British Columbia, and the Arctic; the Athabasca-Mackenzie system is followed by a major shipping route between Edmonton, Alta., and the Arctic. Numerous lakes in the Mackenzie basin act as reservoirs and natural flood controls. The basin, flanked by the Rocky Mts. and the Canadian Shield, is the northern portion of the Great Plains of North America; arctic air masses follow the valley south into the interior of the continent. Much of the Mackenzie valley is heavily forested and, where climate permits, its deep soil is well suited to agriculture. Numerous trading posts were established along the Mackenzie in the early part of the 19th cent. and fur trapping is still an important activity there; the chief trading posts are Fort Simpson, Fort Providence, and Aklavik. The region was the domain of fur traders until the 1930s when vast oil fields and other mineral resources were discovered; Norman Wells is the chief oil-producing town. In the early 1970s large natural gas fields were discovered in the Mackenzie delta region. A plan to construct the Mackenzie Valley Pipeline from the Arctic Ocean to Alberta, which would have been the greatest construction project ever undertaken, was shelved in 1977 after a federal royal commission concluded that, though feasible, the project involved serious legal, political, and environmental problems. Peter Pond was possibly the first European to enter (1777) the Mackenzie drainage area, but Sir Alexander Mackenzie, the 19th-century Canadian explorer, was the first to descend (1789) the river to the Arctic Ocean.

Great River's

Lena

Lena (lē'nu, Rus. lye'nu) [key], river, easternmost of the great rivers of Siberia, c.2,670 mi (4,300 km) long, rising near Lake Baykal, SE Siberian Russia. It flows northeast, then north along the east side of the central Siberian uplands and parallels the Verkhoyansk Range, reaching a width of 8.5 mi (13.7 km). It empties through a c.250-mi- (400-km-) wide delta into the Arctic Ocean. It is navigable for 2,135 mi (3,436 km) upstream; at Yakutsk (915 mi/1,473 km upstream) it is ice free from June to October; at the delta from July to September. Coal and gold are found along the Lena and its tributaries (the Vitim and the Aldan). The Lena was first reached by the Russians in 1630.

Great River's

Amur

Amur (ämoor') [key], Chin. Heilongjiang, river, c.1,800 mi (2,900 km) long, formed by the confluence of the Shilka and Argun rivers, NE Asia, at the Russian-Chinese border; the Amur-Shilka-Onon system is c.2,700 mi (4,350 km) long. The Amur flows generally southeast, forming for more than 1,000 mi (1,610 km) the border between Russia and China, then NE through Russia before entering the Tartar Strait opposite Sakhalin island. Its chief tributaries are the Ussuri, Songhua, Zeya, and Bureya rivers. One of the chief waterways of Asia, the Amur is navigable for small craft for its entire length during the ice-free season (May–Nov.). The chief ports are the Russian cities of Khabarovsk (the head of large craft navigation), Komsomolsk, and Nikolayevsk.

Baykal-Amur Mainline (BAM), railroad line linking central Siberian Russia with the Pacific. The BAM parallels the Trans-Siberian RR but passes north rather than south of Lake Baykal. It is 1,928 mi (3,102 km) long, with 1,987 bridges. Its eastern terminus is Sovetskaya Gavan on the Tatar Strait. It was begun in 1938 but was dismantled for parts after World War II. It was restarted in 1974 and officially completed in 1991. Although it operates along its entire length, it is little used, largely because of a lack of funds to maintain it.

Great River's

Congo

Congo (kong'gō) [key]or Zaïre (zī'ēr, zäēr') [key], great river of equatorial Africa, c.2,720 mi (4,380 km) long, formed by the waters of the Lualaba River and its tributary, the Luvua River, and flowing generally N and W through Congo (Kinshasa) to the Atlantic Ocean.

The second longest river of Africa and one of the longest in the world, the Congo River drains c.1,425,000 sq mi (3,690,750 sq km) including all of Congo (Kinshasa) and parts of Congo (Brazzaville), Cameroon, Central African Republic, Burundi, Tanzania, Zambia, and Angola. The Lualaba River, considered to be the upper Congo River, rises in SE Congo (Kinshasa), flows north over rapids and falls to Bukama, and thence across a vast plain and through a series of marshy lakes (Kabwe, Kabele, Upemba) to receive the Luvua River at Ankoro. The Luvua River has its most remote source in the Chambeshi River, which rises in N Zambia and flows southwest into swamps around Lake Bangweulu; it emerges from the swamps as the Luapula River, continues N along the Congo (Kinshasa)–Zambia border into Lake Mweru, exits from there as the Luvua River, and continues NW to the Lualaba River. A third major headstream is the Lukuga River, which drains from Lake Tanganyika and joins the Lualaba River near Kabalo. From Kabalo, the Lualaba River flows N to Kisangani in a varied course marked by a deep and narrow gorge (the Gates of Hell) below Kongolo, a navigable stretch from Kasongo to Kibombo, a section of rapids and falls from Kibombo to Kindu, a shallow but navigable section from Kindu to Ubundu, and a section of seven cataracts—known as Boyoma Falls—between Ubundu and Kisangani that marks the end of the Lualaba and the beginning of the Congo River proper.

Below Kisangani, the Congo flows west and southwest, in a great curve unbroken by falls or rapids for about 1,090 mi (1,750 km) to Kinshasa. For most of its middle section the Congo is from 4 to 10 mi (6.4–16.1 km) wide, with many islands and sandbars. Because its many large tributaries (including the Lomami, Kasai, Lulonga, Ubangi, Aruwimi, Itimbiri, and Mongala rivers) drain areas with alternating rainy seasons on either side of the equator, the Congo has a fairly constant flow throughout the year. Between Bolobo and Kwamouth the Congo narrows in width to between 1 mi and 1 1/2 mi (1.6–2.4 km) but, c.350 mi (560 km) from its mouth, widens to form lakelike Pool Malebo, on which Kinshasa and Brazzaville are located. From the western end of Pool Malebo, the Congo descends 876 ft (267 m) in a series of 32 rapids, known as Livingstone Falls, to the port of Matadi.

Below Matadi (83 mi/134 km inland) the Congo is navigable by oceangoing vessels and, despite such hazards as the whirlpools of the Devil's Cauldron, shifting sandbars, and sharp bends in the river, forms one of the largest natural harbors in Africa. The river is tidal to Boma, c.60 mi (100 km) upstream. The Congo River enters the Atlantic Ocean between Banana Point, Congo (Kinshasa), and Sharks Point, Angola, and dredging is required to keep a navigable channel open. The river is continued offshore by a c.500-mi-long (800-km) submarine canyon that is c.4,000 ft (1,220 m) deep.

Great River's

Irtysh

Irtysh (irtish') [key], river, c.2,650 mi (4,260 km) long, W Siberian Russia and Kazakhstan. It is the chief tributary of the Ob and one of the two major rivers of W Siberia. As the Ertix, it rises in Xinjiang, China, in the Mongolian Altai Mts., flows NW through Lake Zaysan in Kazakhstan (where it is known as the Ertis), and enters W Siberia. There it receives the Ishim and Tobol rivers, its chief tributaries. The Irtysh flows past Semey in Kazakhstan and Omsk and Tobolsk in Russia and joins the Ob near Khanty-Mansiysk. Major hydroelectric stations are at Öskemen and Zhana Buktyrma, Kazakstan. The river banks were occupied by Chinese, Kalmyks, and Mongols until the Russians arrived in the late 16th cent. The Russian conquest of the basin was completed by the early 19th cent.

Great River's

Paraná

Paraná, river, c.2,000 mi (3,200 km) long, formed by the junction of the Paranaíba and the Rio Grande, SE Brazil. It has the second largest drainage system in South America. It flows generally southwest to its confluence with the Paraguay River, forming the southern border of Paraguay, then S and E through NE Argentina to join the Uruguay River in a huge delta at the head of the Río de la Plata. The lower Paraná is hampered by shifting channels, sandbars, and fluctuating river flow, and is subject to flooding. The stretch along the Brazil-Paraguay border flows in a deep bed and is broken by many waterfalls, now submerged under the large Itaipú Dam, built in the late 20th cent. Downstream at Encarnación, Paraguay, the river is crossed by the Yacyretá dam. The Paraná is the principal commercial artery of interior SE South America. Navigable for oceangoing vessels (via a dredged channel) to Rosario and Santa Fe in Argentina, the Paraná accommodates river craft to the Iguaçu River. A bridge over the river at Foz do Iguaçu links Brazil and Paraguay. The Paraná was first ascended (1526) by Sebastian Cabot, the English explorer in the service of Spain.

Great River's

Yenisei

Yenisei (yenisā', Rus. yenyisyā') [key], chief river of Siberia, c.2,500 mi (4,020 km) long, central Siberian Russia. It is formed at Kyzyl, Tuva Republic, by the junction of the Bolshoi Yenisei and Maly Yenisei rivers, which rise in the E Sayan Mts. along the Russian–Mongolian border. It flows westward, then generally north, past Minusinsk, Krasnoyarsk, Yeniseisk, and Igarka to enter the Kara Sea through a c.250 mi (400 km) long estuary composed of Yenisei Bay and Yenisei Gulf. The Angara, Stony Tunguska, and Lower Tunguska rivers are the Yenisei's chief tributaries. The river is frozen during the winter months. In the spring ice in the upper Yenisei melts before that in the lower river, causing extensive flooding as water backs up behind the frozen portion of the river. The Yenisei's upper course is turbulent, with many rapids, and has a great hydroelectric generating potential; there are giant hydroelectric stations at Krasnoyarsk and at Sayanogorsk. The river's middle course widens and is navigable for steamers. Lumber, grain, and construction materials are transported along the Yenisei. Igarka on the lower river is the region's chief lumber-loading port. There is fishing for sturgeon and salmon in the river's lower reaches.

Great River's

Huang He

Huang He, Hwang Ho (both: hwäng' hoo') [key], or Yellow River,great river of N China, c.3,000 mi (4,830 km) long, rising in the twin lakes Gyaring and Ngoring in the Kunlun Mts., NW Qinghai prov., and flowing generally east into the “great northern bend” (around the Ordos Desert), then east again to the Bohai, an arm of the Yellow Sea.