Mount Durmitor is the hub of Montenegrin mountain tourism, in the winter attracting avid skiers and, increasingly, snowboarders, with hiking and recreational sports taking over in the summer.
The largest of Durmitor's 18 glacial lakes, Crno Jezero consists of two smaller lakes - Veliko Jezero (Big Lake) and Malo Jezero (Small Lake) - connected by a straight so narrow that they are virtually two separate bodies of water.
The Big Lake measures 855m by 615m at most, and boasts a surface area of 338 square kilometers - by far a greater portion of Crno Jezero's total 515 km2 surface. However, it goes no more than 24.5 metres deep, which is less than half the depth of the smaller lake. Thus, with dimensions of 605x400m and a surface area of a mere 177 km2, the Small Lake’s 49.1 metre depth secure for it the greater volume of water.
The origins of the 1,155-metre lake are polygenic. It was created in the Pleistocene by glacial activity in a previously formed doline (Malo Jezero) and a broad cove (Veliko Jezero), both results of karstification. Its water comes from the strong Celina spring and several minor springs along the lake bottom, but mostly from the Mlinski brook, that originates below Zmijinje Jezero.
The other streams that supply the lake water are nameless, appearing periodically when the mountain's snow begins to thaw. The water level varies as much as five meters throughout the year. In times of drought, the level of the Malo Jezero drops more, causing the connecting strait to become a waterfall. When water levels are high, the excess water overflows creating the Žabljačka Reka river, which disappears in sinkholes near Žabljak. Connections have been discovered between Žabljak's sinkholes and springs in the Tara river valley, as well as between Malo Jezero and springs in the Komarnica river valley.
In the summer, Crno Jezero's water temperature is 4 degrees Celsius colder than the outside air, while in winter the lake is frozen about 70 days a year. Three and a half kilometres of hiking trails weave their way along its shores, while another leg of the trail leads all the way to Žabljak's town centre, paving the way to one of Montenegro's favourite recreational areas.