The Duboka drains the eastern side of Kopaonik Mountain. Geomorphology and geology of the area indicate, and the office and field researches confirm, that the Duboka was formerly in the Rasina basin and now belongs to the Toplica system. A minor Toplica tributary captured the Duboka headwater and diverted it into its drainage system. Capturing and captured s of the two systems are a geomorphologic rarity; the headwaters of the Rasina are diverted into the Toplica system, and the middle course of the Toplica (Blatašnica) captures the Rasina.