Ilomska is right tributary of the Ugar river in (Bosnia). It is about 20 kilometres (12 mi) in length, and its source is Vlašić Mountain. It is an essential body of water for surrounding wildlife. Ilomska flows between the Žežnička Greda and Javorak mountains. It has a curved flow around Lisina and Runjavica mountains, through coniferous and mixed spruce-beech woods.