The only longer surface inflow to Lake Cerknica is Cerkniščica river, more than 30 km long, into which waters from the edge of the Otave, Vid and Bloke plateaus collect. Cerkniščica originates in the hilly area of Sveti Vid and Cajnarje, and its outlet flows into Jamski zaliv cove. The upper part of the valley is narrow and deep; from Cajnarje to Begunje the valley floor is wider, flatter and covered with river alluvium. In this part Cerkniščica often floods.
