The Sinanishko Lake (Bulgarian: Синанишко езеро) is a glacial lake in the Pirin mountain range, southwestern Bulgaria, situated about 700 m to the north–northeast of the summit of Sinanitsa (2,516 m) in the small Sinanitsa cirque at an altitude of 2,181 m.[1][2][3] Reaching depth of 11.5 m, it is among the ten deepest lakes in the mountain range.

It has an elongated shape with maximum length of 175 m and a width of 80 m. The surface area is 10,100 m2.

[4] Its waters pour out under the ground and they appear on the surface 120 m away from the lake and form the beginning of the river Sinanishka, a left tributary of the Vlahina reka of the Struma river basin.

[1][4] Close to its northern shores is located the Sinanitsa refuge.