Cardak Lagoon is one of the most important marine environments in the Turkish Strait system, which is home to a variety of organisms. The lagoon is currently under stress and faces the risk of heavy pollution. For this reason, the present state of the lagoon was monitored in this study. During sampling from October 2018 to June 2019, the levels of indicator microorganisms fluctuated up to 4.04 Log(10) cfu 100 ml(-1) and their presence was found to be higher in warmer seasons. The highest positive correlations were observed for total coliform levels with salinity and chemical oxygen demand, whereas the highest negative correlations were found between the levels of fecal coliforms, pH and temperature. E. coli and fecal streptococci showed moderate correlations with the environmental factors in all seasons. Although nitrite and nitrate (NO2 + NO3) were not significantly correlated with bacteria levels, they were present at elevated levels. Cardak Lagoon showed the lowest microbiological and chemical quality in the summer season, and this situation continued into the autumn season as a possible result of increased wastewater discharge and human activities. The lagoon should therefore be monitored regularly and precautions should be taken to prevent severe ecological deterioration.