Water temperature is a hydrologic parameter that affects the changes of lake or sea characteristics. This paper presents analysis of the influence of climatic conditions on the temperature of the lake and the sea. There is written something more about the quality of water, water temperature, air temperature and other meteorological and hydrological parameters and their mutual influence. In the example of Kantrida and Bivio it is presented the influence of climatic conditions on water status, and the relation of certain parameters and their interconnectedness. This paper also presents the overall impact and the reasons for the water quality change of the coastal area. By tearing groundwater into the sea and mixing freshwater with sea water, the seawater temperature changes and destroys the sea quality of these areas. The conditions of Vrana Lake on the island of Cres are also analyzed. Vrana Lake is a unique hydrogeological and hydrological karst phenomenon, and an invaluable water source, with good water quality. There were analyzed the meteorological and hydrological parameters of Vrana Lake and the influence of different parameters on the water temperature of the lake. There are used daily and monthly data values , and the results of the analyzed data are presented and described. Modeling of the water and sea features of the Weka program package, there is used model M5P and Multilayer Perceptron. For the purposes of modeling, there were used data from 2009. to 2016. The main modeling parameter was water temperature. Several variants of the analysis were made where certain parameters were omitted in some variants to obtain a better view of the influence of other parameters on the main parameter. Modeling illustrates the behavior of the Vrana Lake conditions, as well as variations referred to atmospheric influence.