The Tamnava originates from several small streams from the hill of Konjsko brdo (Cyrillic: Коњско брдо; Horse hill) on the northern slopes of Vlašić mountain, northwest of the town of Valjevo, less than a kilometer away from the source of its major tributary, the Ub River.
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The villages of Tamnava, Novaci, Kalinovac, Trlić, Sovljak and Crvena Jabuka are located on the river which has been followed by the satellite flow of the Ub River ever from the source on the Vlašić mountain.