Over the course of a year, a study of the state of the environment was carried out in Pješčana uvala, a settlement near Pula in southern Istria. Pješčana uvala has a problem with wastewater due to the rapid growth and development of the settlement, which has led to debatable interventions in construction, such as the connection of rainwater drains and sewage in certain houses. During heavy rains, it is possible for the reception capacity of the drainage system to overflow and for a mixture of waste and rainwater to flow into the bay. Therefore, the hydrographic and microbiological parameters of the bay were investigated. Of the hydrographic parameters, temperature, salinity, pH and water saturation with oxygen were investigated. Among the microbiological parameters, the concentrations of fecal indicators of Escherichia coli, fecal streptococci and total coliforms and marine autochthonous microbiological indicators were investigated, where the concentrations of autotrophic cyanobacteria and heterotrophic prokaryotes and nanoflagellates were measured. Research has shown seasonal oscillations in the sanitary condition of the bay. It is possible to assume that the cause is an unbalanced rain regime in the area and inadequate infrastructure for receiving and draining rainwater. The highest concentrations of fecal indicators were registered for autumn sampling, when the precipitation in southern Istria is the most abundant. Except for autumn, there was also at least one station with elevated concentrations for winter and summer. The bathing beaches had the lowest FI values, which means that bathers are not at risk. The marine microbiological community had an increased heterotrophic component, which was distributed in the bay like faecal indicators. It can be concluded that heterotrophs fed on organic matter that entered the value with fecal indicators. However, the autotrophic component showed reduced concentrations, most likely because autotrophic organisms interfere with the changes in hydrographic conditions caused by the intake of the water mixture.