Blue Lake

Blue Lake 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. The total depth from the upper rim is around 220 metres, while water depth varies with season. In spring, when the snow from surrounding mountains melts, it can reach 90 m, and in 1914 it reached 114 m, overflowing the southern rim. The lake is a popular destination for hiking and sight-seeing.Maximum dimensions of the lake are around 800 m × 500 m, but they significantly vary due to big changes in the water level. At the end of the summer the lake may completely disappear.In 1907 a road was built descending to the lake. In 1942, an earthquake caused a large rockfall, resulting in reduction of the lake's depth.

Source: Wikipedia