Freshwater Ecoregions of the World
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441: Lower Tigris & Euphrates


Brian Coad, Jennifer Hales


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Species Richness
# of Endemic Species

Major Habitat Type

Temperate floodplain rivers and wetlands


Iran, Iraq, Kuwait, Syria, Turkey, Iraq, Syria


This ecoregion represents the lower Tigris-Euphrates river system. It is bounded by the Zagros Mountains to the east, the Persian Gulf to the south, the deserts of Arabia and Syria to the west, and the Turkish Highlands to the north. Surrounding ecoregions include the Upper Tigris & Euphrates [442] to the north and east and Arabian Interior [440] to the west.

Drainages flowing into

Persian (= Arabian ) Gulf

Main rivers or other water bodies

The dominant rivers are the Tigris and Euphrates rivers with their tributaries on the Mesopotamian plains. Lakes include Tharthar, Razzazza, and Hammar.


Most of the ecoregion is comprised of large marsh and lake areas that are surrounded by a flat landscape which drops 4 cm/km over the lower 300 km of the Euphrates and 8 cm/km along the Tigris. The Tigris and Euphrates meander across the plain and end up partly as an inland delta with extensive marshes near the head of the Persian Gulf. The mean elevation is around 200 m.


The climate of the ecoregion is generally subtropical, hot, and arid. The mean annual temperature is 21.5 ºC, with mean minimum temperatures around 3.5 ºC in winter and mean maximum temperatures over 42 ºC in summer. The mean annual precipitation is 200 mm, but exceeds 700 mm in the mountains to the north and east.   

Freshwater habitats

The lowlands of Iraq, known as Mesopotamia (“land between the rivers”), have extensive marsh and lake habitats fed by the two main rivers. Tributaries of the Tigris originate in the Zagros Mountains. Spring floods feed the marshes and lakes from snow melt. The lakes in central Iraq were saline depressions that were converted to store water for flood control, and now support a fish fauna. The marshes dry out naturally in some years but have been devastated by drainage schemes.

Terrestrial Habitats

This low-lying alluvial plain is surrounded by xeric shrubland and desert, which is often saline. Today, much of the water of the Tigris and Euphrates rivers has been diverted for irrigation, dams, large cities, and intensive agriculture. Vegetation of the marsh areas consists of Phragmites (reeds), Typha (rushes), and Cyperus (papyrus).

Fish Fauna

The fauna is dominated by cyprinids that represent around 75% of the ecoregion’s species. The lower reaches of the basin with brackish water and tidal influence have various marine entrants, of which only three are listed here — bull shark (Carcharhinus leucas), Hilsa shad (Tenualosa ilisha), and yellowfin seabream (Acanthopagrus latus). This basin shares much of its fauna with the Upper Tigris & Euphrates ecoregion [442], but is unique in its extensive marsh and lake habitats.

Description of endemic fishes

There are three endemics in the ecoregion: Glyptothorax steindachneri, Caecocypris basimi, and Iraq blind barb (Typhlogarra widdowsoni). Caecocypris basimi and the Iraq blind barb are endemic genera and species from a cave habitat near Haditha on the Euphrates, and are listed as Vulnerable in the Red List. A near-endemic cyprinid, Hemigrammocapoeta elegans, is probably restricted to the lowlands, as is an undescribed tooth-carp (Aphanius sp.). A sisorid catfish is only known from its original description but may be a synonym.

Other noteworthy fishes

The bull shark (Carcharhinus leucas) once entered the Tigris River as far up as Baghdad.

The fauna is dominated by various members of the genus Barbus, some of which exceed two meters in length. Others are keystone species in the marshes and rivers and have been significant food sources for humans for at least 6000 years.

Other noteworthy aquatic biotic elements

The southern marshes have had distinct mammal and rare bird species, including a smooth-coated otter subspecies (Lutra perspicillatamaxwelli maxwelli) and Bunn’s short-tailed bandicoot rat (Erythronesokia bunnii), both of which are probably now extinct. This area is also highly significant for wintering and breeding waterfowl, and has supported almost the whole world population of the Basra reed warbler (Acrocephalus griseldis) and the Iraq babbler (Turdoides altirostris).

Other noteworthy species include the commercially important shrimp Metapenaeus affinis, which enters the marshes to spawn and feed. The softshell turtle Trionyx euphraticus is probably endangered. Certain prawns and mollusks are evidence of the mingling of African and Oriental taxa. There are also endemic mussels.

Ecological phenomena

Hilsa shad (Tenualosa ilisha) is an important food fish that enters the southern parts of this basin to spawn. Various marine species also enter the southern rivers and marshes, but most are casual visitors. Many freshwater fishes move between the marsh and riverine habitats for spawning, feeding, and overwintering.

Evolutionary phenomena

The cave fishes are important in evolutionary studies as they are depigmented and lack eyes.

Justification for delineation

This ecoregion includes one of the world’s major wetlands with large rivers and formerly extensive marsh habitats. The Shadegan Marshes and associated mudflats in southern Iran is a Ramsar site.

Level of taxonomic exploration



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