Lake Niinsaare () is a lake in Estonia. It is located in the village of Konsu in Alutaguse Parish, Ida-Viru County. On the shore of the lake there is the holiday village of Niinsaare. Lake Niinsaare is located northwest of Lake Nõmme (, also known as ).
The lake has an area of . The lake has an average depth of and a maximum depth of . It is long, and its shoreline measures . It has a volume of .
Lake Niinsaare used to be a closed lake. In 1963, a ditch was dug in Lake Mustjärv (also known as ) from Lake Suurjärv (also known as ), which caused the water level in Lake Niinsaare to drop significantly. By the summer of 1968, at least 50% of the lake was dry.