10. Amur River - China and Russia

Called the "arteries of our planet," rivers have shaped the world for ages, providing habitat and food for wildlife, linking remote cities and villages and providing travel routes for exploration. But the iconic waterways on this list, most of which wind through multiple countries and time zones, are also majestic in their beauty. Click through the pages to learn about the world's 10 longest rivers and how to cruise some of the most important natural wonders on earth.

Stretching for 1,755 miles and located along the border of eastern Russia and northern China, the Amur Riveris the longest undammed river in the Eastern Hemisphere, according to the World WildlifeFund. It originates near the sacred mountain ofBurkan Khaldun in northeastern Mongolia, the birthplace of Genghis Khan, and flowseastward until it connects with the Strait of Tartary. An important symbol of China-Russia relations, the river also spans five distinct ecological regions, from grasslands and boreal forests to desert and tundra, according to InternationalRivers.org.

Several local companies offer tours of the Amur and a glimpse of the cultures that live along the great river, including the Nanay and Ulchi communities. Tour operators such as Nata-Tours also include fishing and picnics on the coast of the Amurin their packages.

NEXT:Ninth longest and the world's deepest river

9. The Congo - Africa

Stretching 2,290 miles, the Congo is the ninth longest river in the world, but it is the world's deepest river with measured depths in excess of 720 ft, according to the U.S. Geological Survey. It is also enormous, winding through the Republic of Congo, the Democratic Republic of Congo, the Central African Republic, Angola, Tanzania, Cameroon, Zambia, Burundi and Rwanda. According to a post on the New York Times, the Congo is "so immense that its source waters in the highlands of eastern Africa take more than six months to exit into the Atlantic Ocean." The river's size, beauty and mystery have made it the perfect backdrop for literary works such as Joseph Conrad's "Heart of Darkness."

Many local tour operators offer Congo River expeditions and safari so visitors can get up close to this mighty natural wonder, andsee the area's villages, plants and forests, and wildlife (the river is home to more than 700 fish species, of which nearly 500 are endemic). Check out tours offered by Safari Guides, Congo Travel and Tours, and Go Congo Tours.

NEXT: A mighty river in South America

8.ParanáRiver -Brazil, Paraguay and Argentina

The Paraná River courses through Brazil, Paraguay and Argentina for 3,032 miles,merging first with the Paraguay River and then farther downstream with the Uruguay River to form the Río de la Plata and emptying into the Atlantic Ocean. Together with the Paraguay, the Parana River provide water and energy for South America's largest city, São Paulo; flood the world's largest wetland, the Pantanal; and thunder over the world's second-largest waterfall, Iguaçu Falls, according to Nature.org.

Tour operators, such as eWaterways, offer small-ship cruises on theParanáRiver and companies suchTafari Travel combine a bike tour of the town of Tigre with a a cruise on theParanáRiverthrough the historic Tigre delta.

NEXT: One of the great Siberian rivers

7. Ob River - Russia

Originating in the Altay Mountains of southwestern Siberia and emptying into the Arctic Ocean, the Ob River, and its major tributary, the Irtysh, stretch for 3,364 miles, making it the seventh longest river in the world.The Ob is used mostly for irrigation, drinking water, hydroelectric energy, and fishing; and for years, the Ob was the only road in or out of a vast region of Siberian wilderness, according to an article in the Christian Science Monitor.

Visitors can visit the Ob River area by heading toNovosibirsk, where there are several nice beaches on the Ob Sea, an artificial lake created by a dam on the Ob River. The city, the third largest in Russia, is a popular stop on the Trans Siberian Railway. It's home to an opera house, theaters and the Central Siberian Botanic Garden, according to the School of Russian and Asian Studies website. There, visitors can also take scenic boat tours on the Ob River.

NEXT: The Mother River of China

6. Yellow River - China

With an estimated length of 3,395 miles, the Yellow River is the sixth longest river in the world.Originating in the Bayankala Mountains in Qinghai province in western China, the river (or​Huang He) flows through nine provinces of China and empties into the Bohai Sea, according to the World Wildlife Fund. This great river is called "Mother River of China," as it is believed to be the cradle of Chinese civilization and the spiritual home of the Chinese people, according to Travel China Guide. Indeed, a cruise through this river is to explore a country's rich history and culture.

Operators such as China Highlights offer multi-day tours of the river and the surrounding forest parks, deserts, grasslands, Hukou Waterfall (the classic Yellow River attraction), the Loess Plateau, and ancient cities.

NEXT: The 'Great River' of Russia

5. Yenisei River - Mongolia and Russia

Stretching 3,443 miles, the YeniseiRiver is the largest river system flowing to the Arctic Ocean and provides power, transportation, food, sport and more to more than a million residents, according to The Atlantic. It is the fifth longest river in the world and is home to 55 native fish species, including two endemics: Gobio sibiricus (a gobionine cyprinid) and Thymallus nigrescens (a grayling), according to Freshwater Ecoregionsof the World.

Tour companies such as Astravel offer tours of the Yenisei River departing from the city of Norilsk in Russia. The river cruise includes stops in villages and towns, including Tutukhansk andYenisseysk, some of the oldest towns in Siberia.

NEXT: The 'Old Man River'

4. Mississippi River - U.S.

The third longest river in America, the Mississippi River flows 2,350 miles from its source at Lake Itasca through the center of the continental United States to the Gulf of Mexico, according to the National Park Service. The Mississippi-Missouri River combination, however, stretches 3,710 miles, making it the fourth longest river in the world. The Mississippi River is one of the most iconic waterways of North America—and an environmental haven.According to the National Wildlife Federation, the Mississippi River Delta has a diversity of habitats—from uplands to the open waters of the Gulf of Mexico, and everything in-between, including wet forests with cypress trees, freshwater marsh, brackish marsh salt marsh and sandy beaches. These habitats support an abundance of migratory and year-round wildlife.

American Cruise Lines offer several options and itineraries for Mississippi River cruises. Their Lower Mississippi River Cruise is a culture- and history-filled 8-day voyage from New Orleans to Memphis, and passengers of their Mississippi River Paddlewheel Cruise can revisit the grand era of steamboatingwith guided shore excursions and chef-prepared regional cuisine.

NEXT: The longest river in Asia

3. Yangtze River - China

With a length of 3,915 miles, the Yangtze River is the third longest river in the world. It is also China's most important water system, culturally, historically and economically.Its banks are home to about 400 million people, or around one-third of the country’s population, and since 1950, the river and its basin “have been the focus of much of China’s economic modernization,” according to Slate.

The Three Gorges Dam on the Yangtze is the largest dam project and hydro-electric power station in the world, generally, people consider the river a dividing line between North China and South China, according to Travel China Guide. It courses from the Tibetan Plateau to the estuary of the East China Sea near Shanghai, creatinga wide range of natural ecosystems that provide vital habitats for species such as the snow leopard, giant panda, and Yangtze finless porpoise, says the World Wildlife Fund.

Travel China Guide has several tours of the Yangtze, ranging from economy to luxury options. Victoria Cruises, an American cruise line, is also sailing the Yangtze, whil eoffering on-board activities, such as lectures on Chinese history and culture, Tai Chi lessons, and calligraphy demonstrations, and led by seasoned river guides.

NEXT: The world's 'River Sea'

2. Amazon River - Brazil, Colombia, Peru

An aerial view of the Amazon river, Amazonas state, Brazil on December 12, 2013. (CHRISTOPHE SIMON/AFP/Getty Images)

Nothing evokes a sense of adventure and mystery like the Amazon. Its sheer size is a wonder: the average discharge of water into the Atlantic Ocean by the Amazon is approximately 175,000 m3 per second, or between one-fifth and one-sixth of the total discharge into the oceans of all of the world's rivers, according to Project Amazonas. And stretching approximately 4,000 miles—from its source in theUcayali-Apurímac river system—across South America, the Amazon River is the second longest river in the world.

The Amazon River is home to amazing biodiversity, the richest of any river in the world. Its waters are populated by 2,500 different species of fish (although scientists believe that there are many more that have not been identified yet), according to Discover Peru. The mighty river is also home to exotic wildlife such as the endangered Amazon River dolphin (or pink dolphin),squirrel-size tamarin monkeys, and three-toed sloths.

With so much to see and experience in the region, it's not a surprise that there's an abundance of cruises and tours of the Amazon River. G Adventures' Riverboat Adventure is led by an Amazon Reserve naturalist guide while Avalon Waterways' Amazon River Cruises brings the comforts of a five-star hotel on a 147 ft-long boat.

NEXT: The world's longest

1. The Nile - Africa

An aerial view shows the Nile river cutting through the Sudanese capital Khartoum on January 13, 2011. (KHALED DESOUKI/AFP/Getty Images)

Stretching for 4,132 miles in northern Africa, the Nile River is the world's longest river, according to the U.S. Geological Survey. Flowing from south to north, the mighty river courses through 10 countries, Uganda, Ethiopia, Sudan, South Sudan, Democratic Republic of the Congo, Kenya, Tanzania, Rwanda, Burundi and ending in Egypt as it feeds into the Mediterranean Sea. It's a true "artery" of Africa. More than 300 million people live in the countries through which the Nile River flows. The waters of the Nile support about 40 percent of Kenya's population, even though just a tenth of semi-arid Kenya is within the Nile Basin, according to Reuters.

The Nile is also teeming with wildlife, the most well-known—and most feared—of which is the Nile crocodile, which lurksalmost totally submerged in the water as they lie in wait for passing prey, says BBC. Hippopotamus, elephants, buffalo, wildebeest, gazelle and other wildlife also use the Nile as a source of water, according to Seven Natural Wonders.

The wildlife of the Nile is just one of the highlights of a river cruise through this iconic water system. Sonesta Nile Cruises offer3-, 4-, and 7-night trips between Aswan and Luxor in Egypt that explore landmarktemples, tombs and ruins in the region. Nile River Cruises offer one-day trips from Bujagali, Uganda aboard their two-story pontoon boat.

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