Sunja is the right tributary of the Sava River, 69 km long.
It springs in Zrinska Gora, at an altitude of 600 m. Previously, it flowed in shallow depressions over a length of about 20 km, flowed slowly and parallel to the Sava, and was recently channelized.
It flows into the Sava opposite the village of Puske, 12 km northwest of Jasenovac, at 91 m above sea level.
The area of its basin is 462 km².
