Many a writer of travelogues, researcher or scientist has felt the urge to describe the shiny surface of the lake, its dark green colour, nearly black because of the depth and surrounding, the thick forest of firs, pines and spruces with moss and blueberries, and the rocks of Međed as if they were holding it in their lap. Science says that it originated in a cirque formed by force of the glaciers from this fan of summits. It actually consists of two lakes, Veliko (Large) and Malo (Small), connected by a narrow isthmus. It is 1.155 m long and 810m, the Large lake has a maximum depth of 26m, the Small lake twice as much, around 50 m! That means that the large lake has twice the surface but nevertheless a lesser volume.
According to the legend, Holy Sava was once passing by, and somebody (for whatever reason) accused him of stealing something. There was no time for defence, the whole village was up on their feet chasing him. Sava somehow managed to flee, but he was so angry that he made a sign of the cross with his rod and commanded the water to flood the village. Now the villagers were fleeing, but the water was reaching them. Those who were running towards the mountains, the water washed away where today the Small lake is located. Where the water reached those rushing into the meadows, today you find the Large lake. The Large lake is filled by a spring at the northwestern side. The Mlinski potok (a brook) is also contributing. But by far the largest amount of water is supplied by Čelina, a system of wells at the slopes of Međed, 25 meters above the Small lake. After hibernation, sometimes already in April and sometimes in June, the Čelina announces the beginning of its "work" noisily. The sudden breakthrough of water is accompanied by a thundering sound. The locals then just say "The Čelina burst out“.
Cascades up to 15 meters high flood the path (there is a 3,5km walking path around the whole lake). The sight is unforgettable, and the braver visitors walk through the foamy curtain. In winter, the lake is covered by a layer of ice for a long time. In summer it warms up to 20 degrees so that it is possible to swim in it. In summer, the water from the Large lake flows into the Small one, in winter through the isthmus (Struga, 60 meters wide) from the Small into the Large lake. There are many miraculous movements. Especially the tangled subterranean effluents. The divided waters of the Black lake, after many kilometers under the whole massive of Durmitor, flow into two rivers, Tara and Piva (bifurcation, a very rare phenomenon), but however, in the end, after a long jurney through the darkness and breakneck waterfalls, they join again at Šćepan Polje, where Piva and Tara meet to form the Drina.