Vrana lake on the island of Cres is the biggest lake among Croatian islands. With its average surface of 5,7 km2 and a volume of 220 million m3, this lake is the biggest cryptodepression in Croatia with the bottom on 61,3 m under the sea level. This lake is specific for its position on the island with the most prominent karst characteristics in Croatia. Therefore, the origin of such big amount of water on generally waterless area, is the topic of many researches. The Vrana lake has the economic value for the islands of Cres and Lošinj – this is its only source for water supply. This paper describes results of hydrological researches on the Vrana lake in period form 2007. till 2017. For clearer understanding the topic of this paper, the first part of the paper describes general characteristics of the Vrana lake and the area around the lake. The short review of the previous researches as well as the problems of lake functioning were given as an introduciton to hydrological researches. Vrana lake is the part of complex hydrological system which functions in harmony with underground karst aquifer which is in balance with the sea. Water pumping for water supply brings imbalance into the system, so observations on the daily basis are needed to keep the lake safe. This paper analyzes the basic hydrological and meteorological parameters on the Vrana lake area: precipitation, air temperature, relative humidity, evaporation from the lake surface, water level, water temperature, pumping, lake inflows and undergronud water level. The result of observing these parameters is the review of the lake condition in the more recent period. The intention is to express importance to keep observing these parameters on the daily basis. The main purpose of this paper is convey the significance of this unique natural phenomenon for the island community and also the importance of lake preservation. Also, the purpose of this paper is to contribute to hydrological understanding of the way the Vrana lake functions.