The Sistan (= Seistan) basin straddles the Iran-Afghanistan border and is a north-west to south-east oval in shape. It comprises a number of minor streams and qanats flowing from the west and the Birjand highlands, but these are rapidly absorbed or run for only a few days each year. Its most obvious feature is the vast hamun or swamp comprising open freshwater lakes, reed beds or neizar, and the rivers that feed the lakes. This is a major oasis of fresh water surrounded by hundreds of kilometres of arid plains. Huntington (1905a; 1905b), Annandale (1919a), Ahmadi and Wossughi (1988), Noorbakhsh (1993), Mansoori (1994), Ibrahimzadeh (1995), Scott (1995), Weier (2002),  CIRSPE (2006a) and van Beek et al. (2008) give descriptions of this basin. Note that Weier's (2002) statement (repeated in various newspaper reports and in UNEP (2003)) that there is nearly 140 species of fish in Sistan is an error by an order of magnitude! The native ichthyofauna comprises a mixture of endemic species, species related to or conspecific with high-altitude species from Central Asia and species from Baluchestan in the wider sense. There is little relationship to species from Iran to the west. Variations in water level and crowded conditions lead to disease and parasite outbreaks in the fishes (Mansoori, 1994).

The principal river is the Helmand (or Hirmand) which flows from the Paghman Mountains just west of Kabul to end in Sistan after a journey of 1400 km. Along with the Hari or Tedzhen, this is the only major river entering Iran. Snow and rain in the Hindu Kush mountains ultimately reaches Sistan at 427 m from heights of 5300 m. The Helmand is the most important river between the Tigris and the Indus and drains an area of 386,000 sq km of which 78,000 sq km or 20.2% lies in Iran (Gleick, 1993).

The Helmand produces 1700-2000 cu m per second in flood and 56 cu m per second in the dry season. The average annual flow is 78 cu m per second. The river varies between 200 and 900 m in width and between 2 and 5 m in depth. The annual water income to Iran is about 6 billion cu m but this varies markedly and was 14,740 million cu m in 1970-1971 and 1976-1977 and 600 cu m in 1985-1986 (Mansoori, 1994). UNEP (2003) gives the following flows in million cu m:-

As it enters the Sistan depression, the Helmand splits into several branches which feed the swamps, the two main ones being the Sistan feeding the Hamun-e Helmand (also Hirmand or Hamun Lake) in Iran and the Parian feeding the Hamun-e Puzak (or Parian) lying mostly in Afghanistan. The northern part of the Hamun-e Helmand is called Hamun-e Sabari, or Lake Sistan, which lies half in Afghanistan and half in Iran, and the southern part is called Hamun-e Hirmand. Hamun-e Sabari receives water from the Farah River and overflow from Hamun-e Puzak. The Hamun-e Hirmand receives water from the southern or Sistan branch of the Helmand River and overflow from Hamun-e Sabari. Other rivers flowing from Afghanistan are the Harut, Khospas and Khash but their flow is minor and intermittent compared to the Helmand (Gabriel, 1938). The whole lake area of Sistan is often called the Hamun Lake.

The plentiful natural flow of the Helmand is reduced by irrigation dams in Afghanistan; the Arqhandab and Kajaki dams extract about half of the 12 billion cu m which enter the Afghan plain (Michel, 1973; Mansoori, 1994; Mojtahedzadeh, 2001). A third dam is under construction in Afghanistan without environmental considerations being taken into account (World Conservation Monitoring Centre, 1990). The proposed Kamal Khan Dam on the Helmand in Afghanistan and the "Sistan Drainage and Irrigation Completion and Rehabilitation Project" in Iran would lower water level in the lake complex. There are also plans to divert water from the Sistan area to the city of Zahedan in the south. The Char-Neimeh (or Chahnimeh) Lake is a depression used as a water reservoir and is filled from the Parian branch of the Helmand. It has a surface area of 4,700 ha and is used for irrigation and fish culture but does reduce flow into the hamuns. However floods in spring 1991 destroyed the Kajaki Dam and associated irrigation controls and the lakes were more extensive than they had been in over a decade. Rainfall in Afghanistan increased flow of the Helmand in 2003 and some flooding was expected in Sistan (www.irna.com, downloaded 23 April 2003). The Helmand was dry at the Iran-Afghanistan border in 2004 (Gall, 2004). Sadeq (1999) lists several factors which are threatening the Hamun Lake namely, fluctuation in incoming water, sedimentation, exotic species, urbanization and increased population pressure on the hamun resources.

The south end of Hamun-e Puzak and the contiguous Hamun-e Sabari (or Lake Hamun) are Ramsar Sites (World Conservation Monitoring Centre, 1990). The Lake Hamun Ramsar Site is on the threatened list of National Parks (Anonymous, 1988b).

Puzak is very shallow, with maximum depth of less than 4 m, and is the first of the Sistan lakes to flood and may never dry out completely unlike the other lakes (Khan et al., 1992; Scott, 1995). This lake has extensive reed beds of Phragmites australis with associated submerged Ceratophyllum demersum and relatively little open water. Reeds are cut as forage for cattle, burnt to improve grazing for livestock, used for boats, for wind-breaks and for cooking and heating. Local people engage in fishing.

The Helmand is very turbid and deposits 8 g of silt for each litre of water (Fisher, 1968). The sediment load in 1975-1976 was 15,149,000 t and in 1985-1986 280,000 t (Mansoori, 1994). Drinking water looks like milk! (personal observations, 1977). Rain accounts for little input to the lake, the annual mean precipitation over 12 years being only 51 mm, most rain falling within 10-15 days (Mansoori, 1994). UNEP (2003) reports evidence of pesticide pollution in the Helmand and the swamps, e.g. dieldrin.

The lake bottom in Iran is clay and silt and the waters are markedly alkaline. Water at the edges of the reed swamp were 31°C in early May, warmer than the inflowing rivers and the irrigation ditches which were only 22°C at this time. Annandale (1919a) and Mansoori (1994) give a brief chemistry of Sistan water. There are marked variations in conductivity, temperature, pH, oxygen, alkalinity and hardness between sites. Conductivity ranges from 1280 to 64,000 mmhos (sic), pH from 7.5 to 9.15, oxygen from 0.64 to 11 mg/l, alkalinity from 3.6 to 165 mval and hardness (CaCO₃) 180 to 3500 mg/l in Mansoori's water samples from the Hamun Lake.

Evaporation lowers the water level each year and is caused by extreme heat and the famous Bad-e Sad-o Bist Ruz (Wind of 120 Days) which approaches 200 km per hour. This wind causes serious erosion and marching sand dunes often block streams causing them to change channel. Evaporation has been measured at 4 m per year because of temperatures over 40°C in July (Mansoori, 1994). Refilling occurs in February-June and in flood years various hamuns are joined together into one vast lake. 75% of flooding occurs in March-May. There are about 3900 sq km of seasonal lake and marsh at a maximum, dropping to 1930 sq km in July-January. The maximum flood zone is about 200 km long and 20 km wide, but the lakes have dried up completely, or almost so, at least 5 times in the past 100 years, e.g. in 1907, 1962 for 5 years, 1970-1971, 1984 for 4 years, 1988-1989, and 1998-2002, with major fish kills resulting (Tate, 1910; Harrington, 1976; Costantini and Tosi, 1978; Anonymous, 1992a; Khan et al., 1992; MacFarquahar, 2001; Foltz, 2002; Weier, 2002; www.netiran.com, downloaded 18 June 2002). There was a big flood in March 1989, spring 1990 and an exceptional flood in February/March 1991 (Khan et al., 1992). The lakes filled in 2005 (E. Penning, pers. comm., 28 July 2005). Mansoori (1994) mentions historical floods, e.g. in 1247 A.D., and droughts, e.g. in 835 A.D. UNEP (2003) gives satellite photographs showing variations in water extent. The fish fauna can recolonise newly-flooded marsh areas from the Helmand but population numbers in the hamun vary greatly between years.

The centre of the hamun is only about 2-3 m deep on average with a maximum depth of 5 m at highest water level (www.bibliothecapersica.com/articlenavigation/index.html, under hamun, downloaded 24 December 2004, gives 11 m). Overflow spills into the salt flat Gowd-e Zereh of Afghanistan through the Shelah River. This flushing effect probably prevents this endorheic basin from becoming saline. The Shelah was reduced to isolated and fishless pools in May 1977. The Gowd-e Zereh is at 467 m at its lowest point.

Extensive canals and ditches form a network over Iranian Sistan and serve to irrigate and drain fields. These waters contain fish, but may dry up. The Hirmand is dammed to feed the major canals. The open lake areas are fringed by reed beds comprised of Typha, Phragmites and Scirpus which are concentrated at the ends of the detrital cones of the river deltas (Costantini and Tosi, 1978). Mansoori (1994) and Ibrahimzadeh (1995) report an absence of Phragmites in area which was two-thirds covered in previous studies, drought being advanced as the causative agent along with cattle grazing (Khan et al., 1992). Usually the reeds recover after drought but in 1991 this did not happen (probably the effects of introduced Ctenopharyngodon idella on the young shoots since fenced areas excluding fish show successful reed growth). Two million fish were introduced in early January 1992 near Kuh-e Khvajeh. Scott (1995) also suggests that local people may have dug up tubers to use as fuel. A major fish and bird kill occurred in November 1994 but the cause was never ascertained (Scott, 1995).

Agricultural land around the Sistan lakes is being abandoned because of increasing soil salinity. Wind-blown salt is becoming a problem in summer and the area might suffer the same fate as the Aral Sea (Scott, 1995). A new road running between the Sabari and Helmand lakes in the Ramsar Site may impede water flow despite bridges having been constructed. A canal between Puzak and Sabari will also have major hydrological impacts.

Curiously, both the open lake and the reed beds are poor in fish but channels among the reeds and areas at the edge of reed beds are productive. The effluents of the Helmand are particularly productive and provide a refuge for fish if the lakes dry out. Annandale in Annandale and Hora (1921) gives an interesting account of the fisheries of the Sistan lakes in the early years of the 20th century. Only one species, Schizothorax zarudnyi, was pursued (q.v.) using reed boats or skiffs called tutin which were still in evidence in the 1970s. The introduction of exotic species resulted in an increased fish catch in the 1980s and 1990s and the number of active fishermen was 1090 (Abzeeyan, Tehran 5(5):III, 1994, M. H. Karim Koshteh, in litt., 2003). However, Ibrahimzadeh (1995) reports that there is no fish catch in the lake. Local people took more fish as the population increased (4% per annum, with added impact from Afghani refugees), as transport facilities improved and as animal husbandry decreased through degradation of reed beds (M. H. Karim Koshteh, in litt., 2003). The Islamic Republic News Agency (IRNA, 22 March 2000) reports a catch of 7000 tonnes from the Hamun Lake; the following figures are from M. H. Karim Koshteh (in litt., 2003):-
 

Year	1990	1991	1992	1993	1994	1995	1996	1997	1998	1999	2000
tonnes	2790	3520	4380	4106	3543	5998	4251	3900	6044	12,000	2426

Meijer (2006) gives an estimated catch in a semi-wet year as high as 21,840 tons although official figures give 9000 t. Variations reflect drought conditions, the year 2000 being particularly severe. Fluctuations in catches make the fishery a difficult occupation. Gilkolaei (2007) estimates a commercial catch of stocked fish at 22.5-45,000 tons/year in the whole Sistan basin.

Sistan has fish farming in various water bodies. In 2005, 1.3 million juveniles of grass carp, common carp, bighead and silver carp produced by the Zahak hatchery were stocked in farms (www.iranfisheries.net, downloaded 17 January 2005; CIRSPE, 2006b). Goldfish and silver carp are exotics found in the hamuns (E. Penning, pers. comm., 28 July 2005). CIRSPE (2006a) also lists Rutilus frisii, Abramis brama and Sander lucioperca, all Caspian Sea basin species, as being present in Sistan but this may be an error. Gilkolaei (2007) discusses breeding of Schizothorax zarudnyi, culture of Ctenopharyngodon idella, Hypophthalmichthys molitrix and Oncorhynchus mykiss and ornamental fish breeding in this basin.

Berg (1940) places this basin in his Sistan District of the Iranian Province. It excludes the upper reaches of the Hirmand River. The schizothoracine fauna is particularly characteristic and had its origins either by descent from higher altitudes during the Pleistocene glaciations (favoured by Berg) or are autochthonous as the forms at high altitudes in the Pamirs and Himalayas rose with mountain building.

Top