Lake Urmia

This page covers the physical water body and its exposed lakebed. “Lake Urmia” is the accepted English heading used by the World Lake Database; the Ramsar record gives “Lake Urmia [or Orumiyeh],” while UNESCO uses “Lake Oromeeh.” These are transliterations of the same lake, not separate features.^[1][2][3]

Three larger or differently bounded areas must not be substituted for open water. The Ramsar site designated in 1975 covers 483,000 ha (4,830 km²) and includes the lake and associated wetland setting. UNESCO's Lake Oromeeh Biosphere Reserve, nominated in 1976, covers 1,142,746 ha (11,427.46 km²). The hydrological basin is about 52,000 km² and extends through West Azerbaijan, East Azerbaijan, and Kurdistan provinces; only the lake shores divide West from East Azerbaijan.^[2][3][8]

The elongated lake occupies the eastern Turkish–Iranian Plateau. Urmia city stands west of the lake and Tabriz east of it. Mountain catchments surround the depression, while broad alluvial plains spread around the principal river mouths in the south and east. Outside the watershed divide, drainage turns toward the Aras–Caspian system to the north and toward the Tigris system to the west and southwest; inside it, surface flow ends at Lake Urmia.^[4][8]

The database coordinate above is useful for placing the lake on a small-scale map, but it cannot locate a mobile edge. UNESCO's nearby coordinate, 37.6254° N, 45.5265° E, locates the much larger biosphere reserve. Neither point defines the lake's limits, which change with stage and with the method used to distinguish shallow brine from wet salt or mud.^[1][3][9]

Lake Urmia occupies an intracontinental tectonic depression associated with the Tabriz and Zarrineh–Rood strike-slip faults. Active deformation organized the basin-scale low, while rivers subsequently filled its margins with alluvial and lake sediment. Volcanic rocks occur around the wider catchment, but the lake itself does not occupy a caldera or simple impact-like bowl.^[4]

The catchment exposes rocks from Precambrian to Quaternary age: volcanic and intrusive rocks, metamorphic and ophiolitic units, carbonate, terrigenous and evaporite-bearing sedimentary rocks, and younger river and lake deposits. That varied bedrock matters hydrologically because weathering supplies different dissolved ions and sediment loads. The Aji Chay, entering from the northeast/east, crosses erodible Neogene evaporite-rich strata and is an especially important source of dissolved ions to the lake.^[4]

A 25 m sediment core records repeated Late Pleistocene and Holocene high and low stands over roughly the past 50,000 years; the chronology becomes imprecise backward in time, so it does not establish one exact “formation date.” Low stands left sulphate-rich sediment or exposed floor, whereas higher stands produced different lake deposits. The modern low stand is capped by salt crust.^[4]

Older summaries commonly describe a roughly 5,000–6,000 km² lake, about 135–140 km long, with mean depth near 5 m. Those figures describe a substantially fuller lake and should not be read as present dimensions. In 2019, field measurements on a regular 5 × 5 km network found a maximum water depth of only 2.35 m, in the northern basin; many coastal cells were too shallow to sample by boat.^[1][4][5][6]

Even a dated area needs a method note. A 2023 review combined in-situ depths with Landsat and Sentinel imagery and found that competing bathymetric models placed the deepest bed about 2 m apart. At water levels below 1,271 m, choices of bathymetry, season, inflow pattern, and satellite water threshold could change estimated inundated area by as much as 950 km². The widest uncertainty occurs around reported levels of 1,270–1,272 m, exactly where shallow water spreads across or withdraws from large peripheral tracts.^[9]

The low-gradient floor explains the striking map response. As stage falls, southern and marginal water breaks into pools, deltas prograde across exposed sediment, salt precipitates, and former islands join one another or the mainland. At higher stands, those same bedrock highs are surrounded by water. Island counts and coastline lengths are therefore stage-dependent observations, not permanent properties.

Lake Urmia is endorheic: water reaches the terminal depression but has no natural surface route to the sea. The Zarrineh Rud and Simineh Rud reach the broad southern margin; the Aji Chay enters from the east; the Mahabad, Gadar, Baranduz, Shahr, Nazlu, Rozeh, Ghaleh, and Zola rivers drain other western and southern sub-basins. Published counts differ because some authors separate perennial from seasonal channels, so this page names the principal mapped inflows rather than treating one river count as definitive.^[4][7][8]

The southern rivers provide more than 90% of reported inflow. Spring runoff raises water and sediment delivery, while dry-season evaporation and reduced discharge favor salt precipitation. Direct precipitation and smaller groundwater inputs also enter the balance, but evaporation is the only natural loss from the lake surface. A 2009 hydrodynamic study used a 50-year mean lake evaporation input of about 1,200 mm yr⁻¹; this is a study-period climatic input, not a current annual measurement.^[6][9]

Climate and water use both matter, and published attribution depends on model period and assumptions. A WaterGAP analysis calibrated with lake volume, river inflow, 284 groundwater wells, GRACE storage, MODIS irrigated area, and local withdrawal data estimated that human water use caused 39–43% of Lake Urmia's roughly 8 km³ loss during 2003–2013 and reduced inflow by 39–45% relative to its naturalized model. The same experiment found that the lake still would not have recovered from the 2008 drought without water use. These percentages are model results for 2003–2013, not timeless shares of every rise or fall.^[8]

Lake Urmia is thalassohaline: sodium and chloride dominate its dissolved ions, giving the brine a broadly seawater-like ionic origin even though evaporation has concentrated it far beyond ocean salinity. A geological synthesis reports 120–380 g L⁻¹ across observations, explicitly varying with location, depth, and season. Fresh inflow dilutes water near river mouths and during wetter periods; falling volume concentrates brine, and evaporation precipitates salt onto the floor.^[4]

The east–west road causeway was built progressively from 1979 to 1992 across 15.4 km of the lake's narrow middle. Its 1.25 km opening connects northern and southern water. It is therefore a restricted passage, not a sealed dam. Three-dimensional modeling found wind to be the main control on circulation, while river discharge, rainfall, and evaporation controlled modeled salinity; the causeway could intensify north–south salinity differences by limiting exchange.^[6]

Wet- and dry-season fieldwork in 2019 found denser northern water and vertical density gradients during the wet season, but stronger wave action and evaporation made the lake more homogeneous during the dry season. The study concluded that the opening does not provide a complete annual balance of water and sediment between the two sectors. This measured seasonal behavior is more precise than treating the causeway as either irrelevant or solely responsible for the lake's contraction.^[5]

The basin has a semi-arid continental climate. A recent geological synthesis reports about 330 mm mean annual precipitation and 9.4°C mean annual temperature for the lake setting, while surrounding elevation produces colder, snowier mountain catchments than the low basin floor. Cool-season rain and snow supply spring runoff; warm, dry conditions increase evaporation later in the year. These controls create seasonal as well as multi-year changes in level and salinity.^[4]

The long decline has not been monotonic. The 2023 hypsometry review separates 2000–2007 mild decline, 2008–2015 sharp desiccation, and 2016–2020 expansion during wetter years and restoration releases. By the end of the 2022 water year, only small ponds remained in the deepest north and near a southwestern river mouth. NASA's Landsat comparison then showed much more water on 8 September 2020 than on 7 September 2023, when most of the mapped basin was exposed salt flat.^[9][10]

Those images are dated observations, not a claim about today's shoreline. Lake area, volume, depth, island connectivity, and salinity should always be paired with an observation date, water level or survey method. A wet-year expansion can cover broad flats quickly without restoring the deeper water volume associated with an earlier high stand.

Lake Urmia belongs in the lake hub as a terminal, hypersaline lake whose physical geography is dominated by shallow bathymetry and changing stage. Lake Van, farther west in Türkiye, is another saline lake within the Turkish–Iranian Plateau, but it occupies a much deeper basin; the comparison helps isolate why Urmia's shoreline and island connections respond so strongly to small vertical changes. The terrain index links Lake Urmia's tectonic depression, deltas, alluvial plains, islands, salt crusts, and exposed lakebed.

1. International Lake Environment Committee, Lake Urmia, World Lake Database record ASI-285, and Iran lake list (accessed 30 August 2026). Source for the accepted English heading, approximate 37.64° N, 45.45° E locator, and legacy 5,960 km² / 5 m mean-depth profile. The record does not date its stage, so this page does not present those morphometric values as current.
2. Convention on Wetlands, Ramsar Sites Information Service, site 38, “Lake Urmia [or Orumiyeh]” (designated 23 June 1975; current database summary accessed 30 August 2026). Source for the official aliases, 37°30′ N, 45°30′ E site locator, 483,000 ha listed area, and the distinction between the designated wetland and changing open water.
3. UNESCO Man and the Biosphere Programme, “Lake Oromeeh” (accessed 30 August 2026). Source for UNESCO's spelling, 1976 nomination, 1,142,746 ha reserve area, 37.6254° N / 45.5265° E reserve locator, and salt-flat, island, wetland, and river-estuary setting.
4. Sarı, S. et al., “Sedimentary evolution and lake level fluctuations of Urmia Lake (north-west Iran) over the past 50,000 years; insights from Artemia faecal pellet records”, Sedimentology 71, 887–911 (2024). Source for plateau position, approximate higher-stage dimensions, 2019 maximum depth, semi-arid climatology, salinity range and ionic class, tectonic setting, catchment geology, Aji Chay solute supply, and dated core evidence. The core chronology is explicitly imprecise back to 50 ka.
5. Mohammadi, A. et al., “Influence of dyke-type causeway on Urmia Lake (NW Iran); insights from water physico-chemical parameters seasonal (2019) changes”, Journal of Hydro-Environment Research 47, 1–14 (2023). Source for the April and September 2019 field design, 5 × 5 km network, 2.35 m measured maximum depth, seasonal density and circulation, and incomplete exchange through the causeway opening.
6. Zeinoddini, M., Tofighi, M. A. & Vafaee, F., “Evaluation of dike-type causeway impacts on the flow and salinity regimes in Urmia Lake, Iran”, Journal of Great Lakes Research 35, 13–22 (2009). Source for the 1979–1992 construction period, 15.4 km embankment, 1.25 km opening, 1,275 m Persian Gulf mean-sea-level model datum, 50-year evaporation input, and modeled circulation and salinity controls.
7. Akbari, M. et al., “Assimilation of Satellite-Based Data for Hydrological Mapping of Precipitation and Direct Runoff Coefficient for the Lake Urmia Basin in Iran”, Water 11, 1624 (2019). Source for the approximately 52,000 km² basin, principal tributary network, terrain division, satellite and station methods, and spatial precipitation context.
8. Hosseini-Moghari, S.-M. et al., “Quantifying the impacts of human water use and climate variations on recent drying of Lake Urmia basin”, Hydrology and Earth System Sciences 24, 1939–1956 (2020). Source for basin extent across three provinces, permanent/seasonal drainage distinction, 1951–2013 climate trend context, and the calibrated 2003–2013 WaterGAP attribution. Percentages in the text are model results, not direct measurements or universal cause shares.
9. Sima, S., Zandsalimi, Z. & Darzi, A., “A review and uncertainty analysis of Lake Urmia's hypsometric relationships”, Journal of Great Lakes Research 49, 102239 (2023). Source for the May 1995–September 2022 level change, southern inflow share, seasonal processes, 2000–2020 phases, field/satellite bathymetry, and quantified uncertainty. The article reports gauge elevations but does not identify their vertical datum.
10. NASA Earth Observatory, “Lake Urmia Shrivels Again” (10 October 2023; accessed 30 August 2026). Landsat 8 OLI and Landsat 9 OLI-2 comparison for 8 September 2020 and 7 September 2023; source for the dated near-dry 2023 observation, not for a current shoreline.