This basin comprises rivers which drain the southern Zagros Mountains to the head of the Persian Gulf, but which are not now tributaries of the Tigris River nor are they the salt streams of Hormozgan. None of these rivers has a significant fishery. At its northern edge, the Zohreh River flows across the Khuzestan plains and is close to Tigris River tributaries. Other major rivers are the Helleh, which debouches into the Gulf north of Bushehr (28°59'N, 50°50'E) and the Mand or Qarah Aqaj (= the classical Sitakos), which, with its tributaries, drains much of Fars Province to the Gulf south of Bushehr. Near Shiraz it is known as the Qarah Aqaj or Kavar River. The Band-e Bahman, a weir or small dam on this river near Kavar, is probably pre-Islamic.

The Mand River is 480 km long and occupies a basin of about 60,000 sq km. Its flow is reduced by a low snow cover (although there can be torrential spring flow), water seepage, evaporation and abstraction for irrigation purposes. Discharge has been estimated to range from 10-2025 cu m (Merchant and Ronaghy, 1976). It is also polluted near Kavar (29°11'N, 52°44'E) by sewage and agriculture residues and does dry up to a series of isolated pools there. A fish kill, numbering in the many thousands, occurred in the Mand near Shiraz in 1977 and was attributed to chemicals used in spraying against malarial mosquitos. The people hired to spray village houses either dumped quantities of the chemical into the river to reduce their work load or washed out containers in the river (Coad, 1980c). Temperature range is at least 20C° between winter and summer. The delta of the Mand is a Protected Area of 46,700 ha. There are thin oxbow lakes and associated marshes

The Mand has a number of tributaries, at least two of which are called Shur (= salt) River. Conductivity near Firuzabad on the Shur River is 695-715 µM/cm but rises to 20,000 µM/cm below salt domes further downriver. The more southerly headwaters are close to those of the Shur River of the Hormozgan basin between Darab (28°45'N, 54°34'E) and Fasa (28°56'N, 53°42'E). The headwaters of the Mand lie north-west of Shiraz near Kuh-e Tabask at 2318 m (29°52'N, 51°49'E) and there are a series of springs in this area called Chehel Chashmeh (= Forty Springs) which feed the Mand. Nearby is the Dasht-e Arzhan (29°39'N, 51°58'E), a small enclosed basin with a flooded plain encompassing about 24 sq km at maximum. It is fed by small springs and streams. The water is fresh since swallow holes in the southeast corner of the plain drain water away with a salt flushing effect. Shiraz was once "chiefly supplied with fish from this lake" (Ouseley, 1819-1823) but it does not now support such a copious ichthyofauna. A report from Reuters (8 June 2000) cites a fish kill numbering in the hundreds of thousands from the "Arjang lagoon, in a suburb of the southern city of Shiraz", presumably this lake, after it dried up (www.iran-sabz.org/news/fish2.htm). The Haft Barm-e Kudian lie about 20 km north of Dasht-e Arzhan at 29°49'N, 52°02'E at 2200 m. The seven lakes lie in rolling country and the largest is about a 1 sq km. Some may dry up in certain years but fish were found suggesting that there is a perennial water supply (Cornwallis, 1968a). Scott (1995) says the southern 5 lakes generally dry out completely in summer. In winter the lakes freeze over. They are about 2-3 m deep and some are slightly saline. These lakes have been stocked with Esox lucius, Hypophthalmichthys molitrix, Ctenopharyngodon idella and Gambusia holbrooki.

Surber (1969) gives some spot data on pH, total alkalinity, calcium-magnesium hardness, chlorides and free CO₂ in the Mand basin. Near Firuzabad, the concentration of total dissolved solids is 333 mg/l while near Jahrom it reaches 6937 mg/l, indicating how there can be great variations in habitat within the same river basin over short distances, depending on local geology.

The Zohreh River and its tributary the Shul, are over 400 km long and have their headwaters near Kuh-e Barm Firuz at 3673 m (30°25'N, 51°58'E) whose northern flank spawns the Khersan River, a Karun tributary in the Tigris basin. Its basin is estimated to be 15,500 sq km. The Kowsar Dam at Gachsaran is 337.5 m high, its crest is 126 m and the reservoir capacity is 450 million cu m (http://netiran.com/news/IRNA/html/941126IRGG10.html). Gorjipoor et al. (2007) carried out a limnological investigation of the Zohreh River.

The Helleh River receives the Dalaki (205 km) and Shapur (231 km) rivers which drain the lower Zagros ranges west of Shiraz. Its basin is estimated to be 20,300 sq km (Shiati (1989) gives 10,000 sq km) and includes Lake Famur. Shiati (1989) gave an account of salinity in the rivers of this basin. Saline springs and salt domes increase the salinity about 10 times as the rivers flow down from the mountains. Total dissolved solids in the upper reaches of this basin are 366 mg/l, rising to 4219 mg/l in the lower reaches. Geological sources of sulphur also add to the chemical make up of these waters. There are no important sources of industrial pollution along these rivers but humans, domestic animals and agriculture are the main pollution sources. The levels of pollution are in the acceptable range (Gh. Izadpanahi, pers. comm., 1995). Aquaculture in the area (Helleh and Mand river basins) has not had obvious effects on coastal water quality (Omidi, 2006). The delta of the Helleh River is a complex of brackish and fresh marshes and lagoons with a maximum depth of 3.5 m. It is the largest freshwater marsh system on the Persian Gulf coast in southern Iran. It is designated as a Protected Area (42,600 ha). This area developed in the early 1970s when the main river channel was diverted onto the coastal plain.

A cave at Bishapur above the Shapur River is reputed to house a deep lake full of fish but this has not been investigated and may only be a local legend (Mounsey, 1872).

Endorheic Lake Famur, Perishan or Parishan (29°31'N, 51°48'E) is a particular feature of the Gulf basin which encompasses 42 sq km at about 820 m near Kazerun, is fed by about 80 fresh and brackish springs with a discharge of about 800 litres/second and supports a fish fauna near the springs. In years of heavy rainfall the fresh areas expand only to contract in dry years.

The ringing marshes are eutrophic and have halophytic plants of the genera Salsola, Kochia, Camphorosma and Halocnemum along with extensive reedbeds of Phragmites communis and Typha. This marshy shore attained 31°C in early June when air temperature was 43°C. Maximum depth is about 6 m, falling in summer to 3.87 m. pH is 7-8. The drainage basin encompasses about 290 sq km. Conductivity is 5 to 6,000 micromhos.

Södergren et al. (1978) recorded pollution in fish from this lake and the Shapur and Kupor rivers. Only small amounts of the organochlorine chemical p,p^'-DDE were found in the lake but the rivers had very high levels of DDT and its metabolites DDE and TDE. At this time DDT was used for indoor spraying against malaria-infected mosquitos and insecticide containers were cleaned in the rivers after spraying.

An account of the lake is given in Farsi by Maafi (1996a; 1996b; 1996c). The lake is eutrophic and low concentrations of oxygen periodically cause fish mortalities. The reed beds are set on fire to increase the available agricultural land and this results in a sediment input with the consequent decrease in water depth, fingerling habitat destruction, and fish mortality through sediments clogging gills. Overfishing is also a problem. Wastewater and sewage enter the lake untreated and this enhances algal growth and eutrophication. Fishery ponds are established west of Lake Parishan resulting in exotic escapes. During periods of low rainfall, Parishan becomes a shallow saline lake and presumably fish habitat is limited to the immediate vicinity of freshwater springs.

Lake Parishan and the nearby Dasht-e Arjan (29°37'N, 51°59'E) are a Ramsar Site (World Conservation Monitoring Centre, 1990). They lie within the Arjan National Park and International Reserve which encompasses 65,750 ha as established in 1973. However the Park has been downgraded to a Protected Area of 52,800 ha with the Ramsar Site being the wetlands of Lake Parishan at 4200 ha and Dasht-e Arjan at 2400 ha (Khan et al., 1992). Dasht-e Arjan at 1950 m is a shallow, eutrophic freshwater lake fed by runoff, precipitation and the Salmon springs. The lake area in winter may be 1950 ha but shrinks in summer to a few hundred hectares. It dried completely in 2001. There is an outflow through swallow-holes in the south-east, traditionally linked to Lake Parishan. The lake margin and the spring-fed marshes have Phragmites communis, Typha and Juncus along with aquatic vegetation. Dasht-e Arjan is cooler than the environs of Lake Parishan because of its higher altitude - 15-35°C in summer and -10-15°C in winter as opposed to 22-40°C and 5-15°C.

As well as the rivers described above, springs and qanats are important in the Gulf basin. The Dalaki mineral springs have a temperature range of 30-38°C and a discharge of 200l/s. They are at 130 m above sea level and their hydrology, geology and chemistry is reviewed in Kompani-Zare and Moore (2001). The fishes in this area have not been investigated.

Rabbaniha et al. (2003) surveyed the larval ichthyofauna in the Farakeh Creek estuary area in the northern Gulf and found 15 families to be represented, Clupeidae, Gobiidae and Sillaginidae making up almost 94% of the catch.

The Shabankareh Dam is a diversion dam in the lower Helleh River basin and several other dams have been planned for this basin. Small canals or diversions are also present in this basin (Borowicka, 1958).

Berg (1940) places this basin, the Hormozgan basin and the Makran basin as part of the Sind Province of the Indian Subregion of the Sino-Indian Region. Its eastwards extent is the lower and middle Indus River. The Iranian portion is called the Southern Iranian District. Small southern Iranian rivers belonged to a single river basin in the Pliocene, facilitating dispersal according to Berg.

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