In this thesis, the physical and chemical parameters of wastewater in the agglomerations of Malinska-Njivice, Krk and Baška were analyzed on the basis of monthly wastewater samples in the period from 2019 to 2023. During this period, the wastewater in these agglomerations was treated with wastewater treatment plants with an upstream treatment stage (mechanical treatment) using long undersea discharge pipes. The wastewater treatment plants have the necessary construction and use permits as well as water law permits that specify the monitoring of wastewater discharge indicators. The aim of this work was to use the available data to show the dependence or independence of the correlation between individual parameters, to determine whether there are deviations in the measured wastewater indicators from the usual values for wastewater quality, to determine the total load of waste materials discharged into the recipient, in this case the sea, and to determine the effects of the discharged wastewater on marine quality. The indicators analyzed were suspended solids, five-day biochemical oxygen demand, chemical oxygen demand, total nitrogen and Kjeldahl nitrogen, total phosphorus, chloride, temperature and pH of the wastewater, as well as the amount of monthly precipitation and the value of monthly wastewater volumes. The analysis of the indicators of the initial data showed that, with the exception of pH and temperature of the wastewater, all values were above the maximum permissible concentration prescribed in the legal document, which was not binding for the municipalities observed at the time, but gives us guidelines for desirable values. The analysis of the data on the quality of the seawater near the observed outfalls also showed that the discharged wastewater does not have a negative impact on the quality of the seawater either near the outfalls or in remote areas. Nevertheless, the conclusion is that for the benefit of the water and the environment, it is necessary to treat the wastewater with equipment that has a higher level of wastewater treatment.