Blue Lake (Croatian: Modro jezero or Plavo jezero) is a karst lake located near Imotski in southern Croatia.

Like the nearby Red Lake, it lies in a deep sinkhole possibly formed by the collapse of an enormous cave.

In spring, when the snow from surrounding mountains melts, it can reach 90 m (300 ft), and in 1914 it reached 114 m (374 ft), overflowing the southern rim.

[3] At the end of the summer the lake may completely disappear.

In 1942, an earthquake caused a large rockfall, resulting in reduction of the lake's depth.