Lake Urmia (Persian: دریاچه ارومیه) is a salt lake in northwestern Iran, in Iranian Azarbaijan (between the provinces of East Azarbaijan and West Azarbaijan), west of the southern portion of the similarly shaped Caspian Sea. It is the largest lake inside Iran, with a surface area of approximately 5,200 km² (2,000 mile²). At its maximum extent, it is about 140 km (87 miles) long, and 55 km (34 miles) wide. Its deepest point is approximately 16 m (52 ft) deep.

The lake is named after the provincial capital city of Urmia, originally a Syriac name meaning city of water. It was called Lake Rezaiyeh (Persian: دریاچه رضائیه) in the early 1930s after Reza Shah Pahlavi, but the lake was renamed 'Urmia' in the mid-1970s. Its ancient Persian name was Chichast. Along with lake Van and lake Sevan, it was one of the three great lakes of the Armenian Kingdom, referred to as the seas of Armenia.