Siutghiol () is a lagoon on the shores of the Black Sea, in ConstanÃÂa County, Northern Dobruja, Romania. It has a length of and a width of ; it extends over and has a maximum depth of .
Ovidiu Island is a small island on the west side of the lake, from the town of Ovidiu. On the east side of the lake is the resort town of Mamaia, which lies on a strip of land in length and only in width, between the Black Sea and Lake Siutghiol.
The name of the lake comes from the Turkish Sütgöl, meaning "the milk lake".