Lake Techirghiol, Protected wetland area in Constanța County, Romania.

Lake Techirghiol is a saltwater lake in Constanța County covering approximately 11.6 square kilometers with a maximum depth of 9 meters. The water body is marked by white salt deposits that form visibly across its surface.

The town of Techirghiol was founded in 1893 on the shore opposite Eforie Nord, and a sanatorium opened there in 1899. The lake's low freshwater inflow raised its salinity to about 95 g/l, which allowed a therapeutic mud layer to form. The town became a treatment resort using the salt water and mud against psoriasis, rheumatism and allergies.

The lake's name originates from Turkish 'Tekirgöl', referring to the white salt patterns that form and become visible on the water surface. Visitors can observe these distinctive markings especially during windy weather.

The lake lies between Eforie Nord and the town of Techirghiol, separated from the Black Sea by a narrow strip of land carrying the DN39 national road (European route E87) and CFR Main Line 800 between Constanța and Mangalia. The town of Techirghiol, on the opposite shore from Eforie Nord, was founded in 1893 and has hosted a sanatorium since 1899.

The mud is sapropelic, formed by bacterial decomposition of Artemia salina crustacean corpses together with the alga Cladophora cristalina. The lake's salinity reaches about 95 g per litre, which allowed this therapeutic mud layer to develop.