The Vrbas river appears at the southern slope of the Vranica mountain, at around 1530 meters above the sea level and it drains central part of the northern slopes of the Dinaric mountain massif. It empties into the Sava river at around 90 meters above the sea level. Total length of the main watercourse is around 235 km.
Average fall of the main course is 6 m/km, which makes it attractive for the hidropower utilization. Its average altitude is around 690meters above the sea level. Total catchment area is approximately 6386 m2. Average annual rainfall is around 800l/m2 at the mouth of the Vrbas to the sava river and up to 1500 l/m2 in the southern part of the basin.
Characteristic mean flow is around 34,6 l/s/km2 Maximum rainfall occurs in the southern parts of the Vrbas basin in the late autumn and winter months, with minimum quantities in summer, whereas the northern parts of the basin receive the largest quantities of rain during the summer months (June-July), with the maximum in November and December.
The most important tributaries are Pliva, Ugar, Crna Rijeka and Vrbanja which are located in the middle part of the basin.
The established available hydropower potential of the basin is 4270 GWh/y of the energy, in the middle-rainy year; out of which, 2510 GWh/y or 58,8% accounts for the main water course and 1760 GWh/y or 41,2% accounts for all tributaries.
Out of totally usable hydropower potential of the catchment area, which is around 3200 GWh, approximately 720 GWh or 22,5% is being used today. This production is realized in the constructed hydropower plants of Jajce I, jajce II and Bočac.