They irrigate our farms, are an important means of transport and a source of eco-friendly power.
Rivers are the life-giving arteries of our planet.
They can be a whole lot of fun for travelers, too.
From exotic wildlife hubs to whitewater rafting hotspots and the most scenic stretches for cruising, we've highlighted 15 rivers worth basing your next trip around.
Rankings were made on five travel criteria.
Scenic beauty -- the physical beauty of the river; waterfalls, color, drama of the landscape.
Nature and wildlife -- diversity and prevalence of flora and fauna.
Culture -- depth, diversity and accessibility of local culture; tribal/medieval villages etc.
Adventure -- thrill factor of the river's topography and location
Activity options -- rafting, wildlife watching, hiking, biking etc.
We've debated among ourselves, researched expert views and polled our colleagues and fellow travelers around the world, to score each river for these qualities.
15. Volga River (Russia)
Scenic beauty: 3 | Nature and wildlife: 2 | Culture: 3 | Adventure: 2 | Activity options: 2
According to an old Russian proverb, to know Russia is to know the Volga.
Winding through the nation's heartland, "Mother Volga" houses 11 of Russia's 20 largest cities on its banks, which explains its popularity among the cruise set.
Most tour boats ply a section of the Volga just north of Moscow before traveling on to St. Petersburg via a series of interconnected waterways, taking in major cities alongside quaint riverside towns sprinkled with historic Kremlins and brightly colored onion-domed churches.
Frozen for three months of the year, the Volga is best visited during the height of summer.
14. Li River (China)
Scenic beauty: 5 | Nature and wildlife: 2 | Culture: 2 | Adventure: 1 | Activity options: 3
China might be known for the Yangtze, but it's difficult not to fall under the spell of the Li (Lijiang) River.
It's possible to take in the river's breathtaking karst topography -- likened to the limestone cliffs of Vietnam's Ha Long Bay -- between the Guangxi Province towns of Guilin and Yangshuo via boat tour, while others prefer to opt for a more traditional bamboo rafting trip along the smaller and less crowded Yulong River (a tributary of the Li), both of which can be organized from Guilin.
13. Loire (France)
Scenic beauty: 4 | Nature and wildlife: 2 | Culture: 3 | Adventure: 1 | Activity options: 2
As European road trips go, it's hard to beat a scenic drive along France's longest river.
As European road trips go, it's hard to beat a scenic drive along France's longest river.
Dotted with grand chateaus steeped in history, sprawling, manicured gardens and undulating green hills stretching to the horizon, the Loire also lends nicely to cruising.
But with no pesky border crossings to account for, most travelers prefer to navigate its length on four wheels, or, thanks to a proliferation of cycle ways, by bike.
Though given the number of vineyards en route, it can be slow going.
12. Colorado River (United States, Mexico)
Scenic beauty: 4 | Nature and wildlife: 2 | Culture: 2 | Adventure: 2 | Activity options: 4
The principal waterway of the southwestern United States, the Colorado River has something for every type of traveler.
Flowing down form the Rocky Mountains, dammed areas including Lake Powell in Arizona, Lake Mead in Nevada and Lake Havasu on the border of California and Arizona are popular house boating, weekend recreation and spring break party destinations respectively, while the section that cuts through the Grand Canyon attracts whitewater rafting enthusiasts, kayakers and tubing fans.
Further south, the river runs through a series of threatened wildlife refuges before drying up in the Mexican desert.
11. Caño Cristales (Colombia)
Scenic beauty: 5 | Nature and wildlife: 3 | Culture: 2 | Adventure: 4 | Activity options: 1
Known as "the river that ran away from paradise," the Caño Cristales in central Colombia is often considered the most beautiful river in the world.
For most of the year, this Orinoco River tributary is virtually indistinguishable from any other.
But during the summer months, when the heat helps resident algae colonies to grow and multiply, the river explodes in a multi-hued array of colors worthy of a thousand photographs.
Off-limits to tourists for many years due to militant activity in the area, the river hub town of La Macarena is now welcoming travelers.
10. Nile (Africa)
Scenic beauty: 4 | Nature and wildlife: 3 | Culture: 4 | Adventure: 3 | Activity options: 2
Though the Nile actually flows through 11 countries, most associate the world's longest river with Egypt.
From the tomb-laden Valley of the Kings to the monumental Temple of Luxor, the riverbanks of the Nile house almost all of Ancient Egypt's historical sites.
A cruise is easily the best way to take them all in at a relaxed pace while watching local life unfold alongside the river much as it has for the past 5,000 years.
9. Rio Futaleufú (Argentina, Chile)
Scenic beauty: 3 | Nature and wildlife: 3 | Culture: 1 | Adventure: 5 | Activity options: 4
Fed by Argentina's glacial lakes, the brilliant aquamarine waters of the Rio Futaleufú cross the Andes and cascade through southeastern Chile, where adrenalin junkies converge from November to March to tackle its heart-quickening rapids by raft or kayak.
Framed by thickets of hardwood forest and sheer granite cliffs, this stunning Patagonian waterway is also a popular sport fishing destination, and hiking, biking, rock climbing and horseback riding are all possible from the scenic Chilean hub town which bears the river's name.
8. Ganges (India, Bangladesh)
Scenic beauty: 3 | Nature and wildlife: 1 | Culture: 5 | Adventure: 4 | Activity options: 3
The world's most populated river basin, "Mother Ganga" certainly isn't the world's cleanest or prettiest waterway, yet it remains India's most sacred river for Hindus.
Witnessing pilgrims converge at the bathing and funeral ghats in the holy city of Varanasi may be one of the most profound travel experiences you'll ever have, but it's safer to swim much further upstream, closer to the Ganges' Himalayan source.
While primarily known as a yoga center, the foothill town of Rishikesh also has a healthy side business in whitewater rafting.
7. Kenai River (United States)
Scenic beauty: 4 | Nature and wildlife: 5 | Culture: 1 | Adventure: 4 | Activity options: 3
Running 82 miles through southern Alaska's Kenai Peninsula, this meltwater river is the most popular sport fishing destination in the state.
Each year there are two salmon runs, which also attract American brown (grizzly) bears along with moose, black bears and multiple bird species.
Beluga whales have also been sighted as far as six miles upstream in the spring.
A scenic, three-hour drive from Anchorage, the Kenai is all geared up for tourism should you fancy opting for a "drifting" wildlife safari, guided glacier walk or multi-day kayaking adventure.
6. Irrawaddy River (Myanmar)
Scenic beauty: 3 | Nature and wildlife: 3 | Culture: 5 | Adventure: 4 | Activity options: 2
If you've already seen the sights along Southeast Asia's majestic Mekong or missed the party in Vang Vieng, Laos' once notorious river tubing party hub, consider a trip to neighboring Myanmar, where river tourism is taking off.
Several international companies now offer river cruises on Myanmar's mysterious Irrawaddy River with varying itineraries taking in ancient temples, remote villages, local trading centers and important Buddhist sites.
5. Danube and Rhine (Europe)
Scenic beauty: 5 | Nature and wildlife: 2 | Culture: 5 | Adventure: 3 | Activity options: 2
Culture and architecture by the water.
The first European river cruises were on the Danube and the Rhine, and for good reason.
Connected by a canal system, the two rivers gurgle through 12 countries between them, with baroque cathedrals, medieval towns and romantic castles a-plenty scattered along their banks.
It's possible to see the most famous section of the Rhine -- between the Middle Rhine towns of Bonn and Bingen -- by ferry in as little as a day if you're pushed for time, though Danube highlights including the city of Melk in Austria, Bratislava in Slovakia, Budapest in Hungary and Vidin in Bulgaria beg for a longer expedition.
4. Sepik River (Papua New Guinea, Indonesia)
Scenic beauty: 3 | Nature and wildlife: 3 | Culture: 5 | Adventure: 5 | Activity options: 2
Referred to as the Amazon of the Asia-Pacific, Papua New Guinea's Sepik River is among the world's most diverse ecosystems.
Winding through alpine heaths, dense tropical rainforests and mangrove swamps before emptying into North PNG's Bismarck Sea, this largely unchartered waterway reaches deep into a world that has remained virtually unchanged for centuries.
River cruises offer an insight into the culture of local communities living so primitively that many old timers can still recall the taste of human flesh from their headhunting days.
3. Río Cahabón (Guatemala)
Scenic beauty: 4 | Nature and wildlife: 3 | Culture: 2 | Adventure: 5 | Activity options: 5
Never heard of it? Few had, until a few years back, when a section of the Rio Cahabón's densely forested pathway through central Guatemala was forged as a key stop on the Central American backpacker trail.
Known as Semuc Champey, the series of spectacular steeped limestone pools bridging over the river are accessed via a hiking trail near the village of Lanquin.
Local hostels also offer tubing excursions along the Rio Cahabón's tributaries, candlelight tours of a cave system carved out by the water, and year-round grade III and IV rafting.
2. Zambezi (Africa)
Scenic beauty: 5 | Nature and wildlife: 4 | Culture: 4 | Adventure: 5 | Activity options: 4
Boasting superb wildlife watching, some of the best white-water rafting on the planet and the thundering beauty of Victoria Falls, the Zambezi is a showstopper.
In the Middle Zambezi, which borders Zambia and Zimbabwe, you can bungee jump off Africa's largest waterfall, or tackle the grade IV rapids just below.
Most wildlife -- from hippo pods to big cats and sly Nile crocodiles -- is spotted on jeep safaris and kayaking trips around the Lower Zambezi, where the swampy delta funnels down through Mozambique into the Indian Ocean.
1. Amazon River (South America)
Scenic beauty: 5 | Nature and wildlife: 5 | Culture: 4 | Adventure: 5 | Activity options: 5
A river that makes a continent.
Topping our list by an aquatic mile, the mighty Amazon snakes through the jungles of nine South American nations, providing a sanctuary for more than 400 indigenous Indian tribes and one in 10 of the known species on earth.
For travelers, the possibilities are huge -- from wildlife spotting safaris to kayaking trips and gnarly jungle treks.
Backpacker-friendly Bolivia is a popular place to explore the pampas by lancha (long-tail boat), stopping off along Amazon tributaries to swim with pink dolphins, fish for piranha and track elusive anaconda.