Vransko jezero is a natural phenomenon of the Riviera of Zadar and the biggest natural lake in Croatia with surface of 30,7 km2. It gets its water from several springs, and it goes through the abyss and 800 m long channel of Prosika from the lake to the bay of Pirovac. Vransko jezero offers many interesting things: it is protected as an ornithological reservation, it has a small colony of herons and it is a resort of many species of swamp birds. Freshwater fishery is also interesting, considering the distance from the sea. In the north the are ruins of the fortress of Vrana and the medieval Turkish seraglio.