Lake Urmia (Persian: دریاچه ارومیه, Daryache-ye Orumiye, Azerbaijani: Urmu gölü اورمو گؤلو, Kurdish, Zarivar-i Wermy, Armenian: Ուրմիա Լիճ, "Urmia Lij"; ancient name: Lake Matiene) is a salt lake in northwestern Iran near Iran's border with Turkey. The lake is between the Iranian provinces of East Azerbaijan and West Azerbaijan, west of the southern portion of the similarly shaped Caspian Sea. It is the largest lake in the Middle East, and the third largest saltwater lake on earth, with a surface area of approximately 5,200 km² (2,000 mile²), 140 km (87 mi) length, 55 km (34 mi) width, and 16 m (52 ft) depth.It is protected as a national park by the Iranian Department of Environment.
The main cations in the lake water include Na+, K+, Ca2+, Li+ and Mg2+, while Cl–, SO42–, HCO3– are the main anions. The Na+ and Cl– concentration is roughly four times the concentration of natural seawater. Sodium ions are at slightly higher concentration in the south compared to the north of the lake, which could result from the shallower depth in the south, and a higher net evaporation rate. The lake is divided into north and south, separated by a causeway in which a 1,500 m gap provides little exchange of water between the two parts. Due to drought and increased demands for agricultural water in the lake's basin, the salinity of the lake has risen to more than 300 g/litre during recent years, and large areas of the lake bed have been desiccated.