[2] Several kilometers before the convergence with the Drina, the river has created a deep limestone gorgelike canyon with vertical cliffs.

Both major tributaries, Tribuća and Sušica, flow into the Trešnjica in the canyon, which is 6 km (3.7 mi) long.

[2] The area is a designated nature reserve of which the largest part is covered with forests and thickets of common hornbeam, turkey oak, black pine and juniper.

[3][4][5][6] Many birds of prey nest in the Trešnjica gorge, including golden eagle, common kestrel, goshawk and sparrow hawk.

Trešnjica is the location of the northernmost habitat of griffon vulture and only second region in Serbia inhabited by the bird, after the Uvac canyon.