__NOTOC__ The Iguazu River ( ,  ; also called Rio Iguassu) is a river in Brazil and Argentina.
It is an important tributary of the Paraná River.
The Iguazu River is  long, with a drainage basin of .
Course
The Iguazu originates in the Serra do Mar coastal mountains of the Brazilian state of Paraná and close to Curitiba.
For , to its confluence with the San Antonio River, the Iguazu flows west through Paraná State, Brazil.
Downriver from the confluence the Iguazu River forms the boundary between Brazil and Argentina's Misiones Province.
Continuing west, the river drops off a plateau, forming Iguazu Falls, which are accessible via the Rainforest Ecological Train.
The falls are within national parks in both Brazil, Iguaçu National Park, and Argentina, Iguazú National Park.
It empties into the Paraná River at the point where the borders of Argentina, Brazil, and Paraguay join, an area known as the Triple Frontier.
Ecology
Unlike tropical South American rivers where the annual variations in temperature are relatively limited, the water in the subtropical Iguazu River varies significantly depending on season.
At two sites, one located just above and another just below the falls, the water at both varied from about , and average was just below .Nardelli, Bueno, Ludwig, and Guimarães (2016).
Structure and dynamics of the planktonic diatom community in the Iguassu River, Paraná State, Brazil.
Braz.
J. Biol.
76(2).
The pH is typically near-neutral, ranging from 5.9 to 8.7.
About 100 fish species are native to the Iguazu River and several undescribed species are known.Daga, Debona, Abilhoa, Gubiani & Vitule (2016).
Non-native fish invasion of Neotropical ecoregion with high endemism: a review of the Iguaçu River.
Aquatic Invasions 11(2): 209-223.Baumgartner, Pavanelli, Baumgartner, Bifi, Debona & Frana (2012).
Peixes do baixo rio Iguaçu.
EDUEM.
DOI:10.7476/9788576285861 Most fish species in the river are catfish, characiforms and cichlids.Piálek, Dragová, Casciotta, Almirón & Řičan (2015).
Description of two new species of Crenicichla (Teleostei: Cichlidae) from the lower Iguazú River with a taxonomic reappraisal of C. iguassuensis, C. tesay and C. yaha.
Historia Natural 5(2): 5-27.
About 70% are endemic, which to a large extent is linked to the falls, serving both as a home for rheophilic species and isolating species above and below.
This also means that, with the exception of the threatened Steindachneridion melanodermatum in the lower part, large migratory fish known from much of the Paraná River Basin are naturally absent from Iguazu.Freshwater Ecoregions of the World (2010): Igussu.
Retrieved 28 July 2016.
Almost 30  introduced species are found in the river where about one-third originate from other continents (such as carp, largemouth bass,  tilapia and African sharptooth catfish) and the remaining from elsewhere in South America (such as  dorado, Cichla kelberi, pacu, Brycon hilarii, Prochilodus lineatus and Odontesthes bonariensis).Ferrareze & Nogueira (2015).
Impact assessment of the introduction of Cichla kelberi in a large Neotropical reservoir and its lateral lagoons (Upper Paraná River Basin, Brazil).
Braz.
J. Biol.
75(4).Gubiani, Frana, Maciel & Baumgartner (2010).
Occurrence of the non-native fish Salminus brasiliensis (Cuvier, 1816), in a global biodiversity ecoregion, Iguaçu River, Paraná River basin, Brazil.
Aquatic Invasions 5 (2): 223-227.
The unusual Aegla crustacean are locally common in the Iguazu River Basin.Cyrino, Bureau & Kapoor, editors (2008).
Feeding and Digestive Functions of Fishes.
p.
45. Science Publishers.
Environmental issues
In July 2000 more than  of crude oil spilled into the river from a state-run oil refinery in the municipality of Araucária near Curitiba.
See also
List of rivers of Paraguay
List of rivers of Brazil
References
