The source of river Ploucnice is situated about two kilometers from the village Osecna close to Straz pod Ralskem. It lies in a thick leafy forest. Ploucnice flows from Straz pod Ralskem via the village Noviny among high limestone rock faces. Then he turn to about 13 meters high and 3,5 meters wide cut tunnel. A way through an open gullet follows as well as via a long rock corridor. Both corridors are artificial and the water stoppage is made by five weirs embedded to the rock. This place is called “Prurva Ploucnice” (the Ploucnice gash).