This is a list of the longest undammed rivers of the world, ordered by length.
| River | data-sort-type = number | Length | data-sort-type = number | Drainage area | data-sort-type = number | Average discharge (m³/s) | Mouth | Notes | Reference | Rank | |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Amazon River | 6937km (4,310miles) 6992km (4,345miles) | 7050000km2 | 219000m3/s | Atlantic Ocean | Second-longest and largest river in the world, undammed as well as unbridged, does not form a delta while joining the sea due to adequate thrust of river water to overcome the sea water wave and tidal thrusts. | 1 | |||||
| Lena River | 4472km (2,779miles) | 2500000km2 | 17000m3/s | Arctic Ocean | Longest undammed river in Asia. | 2 | |||||
| Amur - Shilka - Onon | 4197km (2,608miles) | 1855000km2 | 11700m3/s | Strait of Tartary | 3 | ||||||
| Mackenzie - Slave - Athabasca | 3403km (2,115miles) | 1805200km2 | 10700m3/s | Arctic Ocean | The Peace - Finlay system would extend even longer from the head of the Slave but there are dams on the Peace. | 4 | |||||
| Nizhnyaya Tunguska River | 2989km (1,857miles) | 473000km2 | 3680m3/s | Yenisei River | The Russian government is planning to build hydro dams on the river within the next few years. | 5 | |||||
| Salween River | 2815km (1,749miles) | 324000km2 | 6700m3/s | Andaman Sea | Longest undammed Southeast Asian river. Burma is planning to build the Tasang Dam and several others. | 6 | |||||
| Paraguay River | 2549km (1,584miles) | 1150000km2 | 4550m3/s | Paraná River | 7 | ||||||
| Amu Darya - Panj | 2500km (1,600miles) | 534700km2 | 1330m3/s | Aral Sea (former) | Although undammed, heavy diversion through canals causes the river to frequently dry up without reaching its mouth. Tajikistan is planning to build a hydroelectric dam on the Panj River. | 8 | |||||
| Aldan River | 2273km (1,412miles) | 729000km2 | 5060m3/s | Lena River | |||||||
| Rio Negro | 2230km (1,390miles) | 691000km2 | 29300m3/s | Amazon River | |||||||
| Vitim River | 1978km (1,229miles) | Lena River | |||||||||
| Indigirka River | 1726km (1,072miles) | 360400km2 | 1810m3/s | Arctic Ocean | |||||||
| Fraser River | 1375km (854miles) | 220000km2 | 3475m3/s | Pacific Ocean | |||||||
| Kuskokwim River | 1165km (724miles) | 120000km2 | 1900m3/s | Bering Sea | |||||||
| Back River | 1150km (720miles) | Arctic Ocean | |||||||||
| Anadyr River | 1150km (720miles) | 191000km2 | 2020m3/s | Gulf of Anadyr | |||||||
| Liard River | 1115km (693miles) | 277100km2 | 2434m3/s | Mackenzie River | |||||||
| Yellowstone River | 1114km (692miles) | 181300km2 | 380m3/s | Missouri River | Longest undammed river in the contiguous United States. | ||||||
| Maya River | 1053km (654miles) | 171000km2 | 1180m3/s | Aldan River | |||||||
| Fly River | 1050km (650miles) | 76000km2 | 6500m3/s | Gulf of Papua | Largest completely undammed river system in the world | ||||||
| White River | 934km (580miles) | 26000km2 | 16m3/s | Missouri River | |||||||
| Tanana River | 916km (569miles) | 113960km2 | 1172m3/s | Yukon River | |||||||
| Thelon River | 900km (600miles) | 142400km2 | Hudson Bay | ||||||||
| Salmon River | 684km (425miles) | 36000km2 | 310m3/s | Snake River | |||||||
| Stikine River | 610km (380miles) | 52000km2 | 1580m3/s | Pacific Ocean | |||||||
| Skeena River | 570km (350miles) | 54400km2 | 1760m3/s | Pacific Ocean | |||||||
| Susitna River | 504km (313miles) | 52000km2 | 1400m3/s | Pacific Ocean | Alaska is planning to build a hydroelectric dam on the river at Devil's Canyon. |