This is a list of the largest river basins without fragmentation by dams in their catchments, ordered by average annual discharge.
To qualify for inclusion, a river must not only have no dams on its “main” stem, but also no dams on any tributary. For this reason, major world rivers such as the Amazon, Lena, Irrawaddy, Amur, and Fraser are disqualified because of dams on tributary streams.
Many of the rivers in this list have uncertain discharges. With the exception of those in Russia, streamgauges have seldom (if ever) been placed on the majority of the largest unfragmented river systems, due to the remoteness and/or ruggedness of the terrain in which they are located. Apart from the Fly which is clearly the largest, all ranks listed here are not perfectly certain, and there also exist a number of rivers in Sundaland that might qualify with reliable discharge data, such as the Kapuas.[1]
| Rank | River | Basin countries | Length of longest channel | Drainage area | Average discharge (m3/s) | Average annual discharge | Mouth | Notes | |
|---|---|---|---|---|---|---|---|---|---|
| 1 | Fly | Papua New Guinea Indonesia | 1050km (650miles) | 76000km2 | 7000m3/s | 220km3 | Gulf of Papua | Largest river with no dam in its catchment[2] | |
| 2 | Mamberamo | Indonesia | 1112km (691miles) | 78992km2 | 5500m3/s | 170km3 | Pacific Ocean | Indonesia's second largest river after the Kapuas.[3] | |
| 3 | Sepik | Papua New Guinea Indonesia | 1126km (700miles) | 80321km2 | 5000m3/s | 157.7km3 | Pacific Ocean | Often regarded as largest completely pristine river system in the world[4] | |
| 4 | Pechora | Russia | 1809km (1,124miles) | 322000km2 | 4533m3/s | 143.1km3 | Arctic Ocean | Once the subject of a possible transfer of water into the Volga. | |
| 5 | Atrato | Colombia | 750km (470miles) | 38600km2 | 4140m3/s | 131km3 | Caribbean Sea | Some estimates place discharge much higher - possibly placing the Atrato second only to the Fly[5] [6] | |
| 6 | Kaladan | Burma India | 350km (220miles) | 30500km2[7] | 3476m3/s | 110km3 | Bay of Bengal | Discharge estimated in absence of streamgauges. Dredging project by Indian and Myanmar governments. | |
| 7 | Kikori | Papua New Guinea | 320km (200miles) | 23300km2 | 3274m3/s | 103km3 | Gulf of Papua | ||
| 8 | Khatanga | Russia (Krasnoyarsk Krai) | 1150km (720miles) | 364000km2 | 3200m3/s | 101km3 | Arctic Ocean | Most northerly large river system in the world, with northernmost tree line in basin. | |
| 9 | Purari | Papua New Guinea | 470km (290miles) | 33670km2 | 3000m3/s | 95km3 | Gulf of Papua | Hydroelectric dam proposed by Queensland government, so may need to be removed from list[8] | |
| 10 | Pyasina | Russia (Krasnoyarsk Krai) | 818km (508miles) | 182000km2 | 2260m3/s | 71km3 | Arctic Ocean | Norilsk, most northerly city over 100,000, located on main stem of river. | |
| 11 | Essequibo | Guyana Venezuela | 1000km (1,000miles)[9] | 69000km2 | 2213m3/s | 70km3 | Caribbean Sea | Largest completely unfragmented river flowing into Atlantic. | |
| 12 | Anadyr | Russia | 1150km (720miles) | 191000km2 | 2020m3/s | 64km3 | Gulf of Anadyr | ||
| 13 | Kuskokwim | Alaska (United States) | 1165km (724miles) | 120000km2 | 1900m3/s | 60km3 | Bering Sea | Largest unfragmented river in North America. Small dams exist on tributaries of Yukon, with which it shares a major delta. | |
| 14 | Indigirka | Russia (Sakha) | 1726km (1,072miles) | 360400km2 | 1810m3/s | 57km3 | Arctic Ocean | Oymyakon, often thought of as the Northern Pole of Cold, located on main stem of river. | |
| 15 | Great Tenasserim | Burma | 300km (200miles) | 17673km2 | 1788m3/s | 56km3 | Andaman Sea | Discharge estimated in absence of streamgauges. | |
| 16 | Copper | Alaska (United States) | 460km (290miles) | 63000km2 | 1700m3/s | 54km3 | Pacific Ocean | ||
| 17 | Stikine | Canada Alaska (United States) | 539km (335miles) | 52000km2 | 1600m3/s | 51km3 | Pacific Ocean | ||
| 18 | Taz | Russia | 1401km (871miles) | 150000km2 | 1540m3/s | 49km3 | Kara Sea | ||
| 19 | Courantyne | Suriname Guyana | 765km (475miles) | 69000km2 | 1500m3/s | 47km3 | Atlantic Ocean | ||
| 20 | Susitna | Alaska (United States) | 504km (313miles) | 63400km2 | 1400m3/s | 44km3 | Pacific Ocean | Hydropower dams proposed at present, so may not remain on list indefinitely[10] | |
| 21 | Thelon | Canada (Nunavut) | 900km (600miles) | 239332km2 | 1380m3/s | 44km3 | Chesterfield Inlet | ||
| 22 | Chari | Chad Cameroon Central African Republic | 949km (590miles) | 548747km2 | 1200m3/s | 38km3 | Lake Chad | Only dryland river with discharge over 10km3 not affected by dams. | |
| 23 | Olenyok | Russia (Sakha) | 2270km (1,410miles)[11] | 219300km2 | 1090m3/s | 35km3 | Arctic Ocean | ||
| 24 | Kamchatka | Russia | 758km (471miles) | 56300km2 | 1050m3/s | 33km3 | Pacific Ocean | ||
| 25 | Laluai | Papua New Guinea (Bougainville Island) | 35km (22miles) | 464km2 | 40m3/s | 1.3km3 | Pacific Ocean | Hydropower dams proposed at present,[12] so may not remain on list permanently |