Lake "Kidney" is emblematic of the Seven Rila Lakes, as well as of Rila and Bulgaria in general. It has a very characteristic shape - it looks exactly like a kidney.

It is located at an altitude of 2282 m and is 28 m deep. The catchment area is 0.54 sq. km. The water surface area 85 acres. The water volume is 1170 thousand m³. The area of the lake is 85 decares.

It is the second largest and deepest lake of the Seven Rila Lakes group. It is the second deepest after the Eye. In the recent past, the lake was called Kara gol.