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.
Continent color keyAfricaAsiaEuropeNorth AmericaOceaniaSouth America
Annual discharge color keyOver Less than
RankRiverBasin countriesLength of longest channelDrainage areaAverage discharge (m3/s)Average annual dischargeMouthNotes1FlyPapua New GuineaIndonesiaGulf of PapuaLargest river with no dam in its catchment2MamberamoIndonesiaPacific OceanIndonesia's second largest river after the Kapuas.3SepikPapua New GuineaIndonesiaPacific OceanOften regarded as largest completely pristine river system in the world4PechoraRussiaArctic OceanOnce the subject of a possible transfer of water into the Volga.5AtratoColombiaCaribbean SeaSome estimates place discharge much higher - possibly placing the Atrato second only to the Fly6KaladanBurmaIndiaHooper, Bruce Peter; Integrated River Basin Governance: Learning from International Experiences; p. 286. Bay of BengalDischarge estimated in absence of streamgauges.Dredging project by Indian and Myanmar governments.7KikoriPapua New GuineaGulf of Papua8KhatangaRussia (Krasnoyarsk Krai)Arctic OceanMost northerly large river system in the world, with northernmost tree line in basin.9PurariPapua New GuineaGulf of PapuaHydroelectric dam proposed by Queensland government, so may need to be removed from list10PyasinaRussia (Krasnoyarsk Krai)Arctic OceanNorilsk, most northerly city over 100,000, located on main stem of river.11EssequiboGuyanaVenezuelaRongxing Guo; Territorial Disputes and Resource Management: A Global Handbook; p. 109. Caribbean SeaLargest completely unfragmented river flowing into Atlantic.12AnadyrRussiaGulf of Anadyr13KuskokwimAlaska (United States)Bering SeaLargest unfragmented river in North America.Small dams exist on tributaries of Yukon, with which it shares a major delta.14IndigirkaRussia (Sakha)Arctic OceanOymyakon, often thought of as the Northern Pole of Cold, located on main stem of river.15Great TenasserimBurmaAndaman SeaDischarge estimated in absence of streamgauges.16CopperAlaska (United States)Pacific Ocean17StikineCanadaAlaska (United States)Pacific Ocean18TazRussiaKara Sea19CourantyneSurinameGuyanaAtlantic Ocean20SusitnaAlaska (United States)Pacific OceanHydropower dams proposed at present, so may not remain on list indefinitely21ThelonCanada (Nunavut)Chesterfield Inlet22ChariChadCameroonCentral African RepublicLake ChadOnly dryland river with discharge over not affected by dams.23OlenyokRussia (Sakha)Arctic Ocean24KamchatkaRussiaPacific Ocean25LaluaiPapua New Guinea (Bougainville Island)Pacific OceanHydropower dams proposed at present,Oxford Business Group; The Report: Papua New Guinea 2012 so may not remain on list permanently
See also List of longest undammed rivers
References Nilsson, Christer; Reidy, Catherine A.; Dynesius, Mats and Revenga Carmen; “Fragmentation and Flow Regulation of the World's Large River Systems”; in Science; 15 April 2005: Vol. 308 no. 5720 pp. 405–408; DOI: 10.1126/science.1107887 Nuttall, Mark (editor); Encyclopedia of the Arctic