Lopača near mouth (in Vrbanja)
|Country||Bosnia and Herzegovina|
|- location||Selačka planina|
|- elevation||1090 m|
|Length||5 km (3.1 mi)|
|Basin size||Black Sea|
Lopača is one of many right tributaries in the upper flow of Vrbanja (Bosnia and Herzegovina). Lopača has its source from two components (small streams) in the eastern slopes of Selačka Mountain, between the hills Marina Glava (1192 m) and Lujin Dirjek (1180 m). These components of the source meet at about 1090 m. ·  In the upper part of its course, Lopača flows towards the southwest, then it goes to the northwest, then just before its confluence to Vrbanja, redirects again to the southwest.
Lopača flows below the village of Gelići, along the slopes of Melina (north) and Osoje (south). It flows into Vrbanja at an altitude of 566 m, under the slopes of Previja with the summit of Padališće (785 m). On each side, it receives water from six streams and small streams, the largest of which (right) is Dolovi. It also receives water from several coastal sources, which keeps its water level relatively stable even during the longest periods of drought.
Below the village of Gelići until its confluence, in the 1960s, there were 20 watermills on Lopača.