After a total underground flow of some , the waters of the sinking Fatnička reka re-appear as a series of very powerful cave springs near the town of Bileća, which are joined into one river, the Trebišnjica, the most important river in eastern Hercegovina.
The Trebišnjica turns west between the villages of Donje Grnčarevo and Lastva into the Trebinjsko polje (Field of Trebinje), being dammed once again at the village of Gorica, with a small reservoir.