This study aimed to investigate water level fluctuations on water physiochemical, nutritional, and microbial parameters of the Gorgan Bay and Miyankaleh wetland from 2012 to 2021. To determine changes in water body area, NDWI was calculated from Landsat 7 and 8 satellite images. The effect of water level fluctuations on changes in pH, electrical conductivity, salinity, dissolved oxygen, temperature, turbidity, nitrate, phosphate, ammonia, fecal coliform, and total coliform was analyzed among various years. Regression relationships between changes in water body area and the studied parameters were checked and the best-fitted model was selected. Based on the water body area calculation, three different water levels were detected: 1-low water level (2012-2016), 2-water reduction transition period (2017-2018), 3- water stress period (2019-2021). The effects of first and third water reduction periods were significant on changes in pH, electrical conductivity, salinity, dissolved oxygen, turbidity, phosphate, and ammonia (p<0.05); although they were not significant on total dissolved solids, nitrate, and microbial parameters (p>0.05). Logarithmic and quadratic relationships were identified as the best-fitted models describing the association between the variables under investigation and water level fluctuations during the studied period, which might be influenced by seawater inflow through the connecting channel, local rivers, atmospheric precipitation, agricultural runoff, municipal waste, and the chemical composition of the sediment and the bay floor. Given the impact of water level fluctuations on physiochemical and microbial characteristics of the bay water, it is recommended to implement some more in-depth studies on changes in biodiversity and species richness in the bay