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
Recent events may have forced most travelers to put a trip to Egypt on the backburner, but fortunately the world's longest river -- which shares its resources with 10 other countries -- isn't going anywhere.
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.