In recent years, assessing surface water quality using biological indices has attracted attention as an effective and cost-efficient method for environmental monitoring. In this study, the water quality of the Shahab River and areas leading to the Nematabad Dam, located in the northwest of Asadabad (Hamadan Province, Iran), was evaluated using geochemical analyses and biological indices. Biological sampling was conducted at 19 stations along the river, and water samples were collected from 11 stations. Chemical analysis focused on major elements, including calcium, magnesium, sodium, and potassium, as well as heavy metals such as zinc, iron, and copper. According to the Scree plot, the most abundant elements in the region’s waters were sodium, potassium, magnesium, and manganese, most likely originating from the geological characteristics of the area. In the biological assessment, over 3,000 gastropod specimens from five species were identified. The results suggest that gastropods exhibited higher abundance and diversity upstream of the river and farther from the Nematabad Dam. However, establishing a statistically significant relationship between water resources and gastropod populations requires further time, studies, and analyses. Overall, the findings indicate that freshwater gastropods can serve as sensitive bioindicators for evaluating the quality of aquatic resources.