This study investigates the presence of microplastics (MPs) and heavy metal contamination in the Nida River in Poland. The research analyzed MPs, heavy metal concentrations, and physicochemical properties of water samples collected from five locations along the river. The results showed a wide range of MPs, including fibres, fragments, pellets, and foams, with an average of 245 ± 21 MPs per litre. The MPs varied in size, with an average size of 2852 ± 899 micrometers. The study also identified various heavy metals, with zinc having the highest average concentration at 96.86 ± 40.25 µg/L, followed by lead at 37.6 ± 31.9 µg/L. The water samples exhibited fluctuations in heavy metal levels, with pH, turbidity, and conductivity values also being measured. The health risk assessment indicated that the HQ and HI values for adults and children were below one, suggesting a low non-carcinogenic risk. However, the carcinogenic excess lifetime cancer risk (ELCR) exceeded the threshold value in most samples. The study highlights the importance of monitoring MPs and heavy metal contamination in freshwater sources to ensure water quality and human health. The findings emphasize the need for effective pollution management and water quality standards to protect aquatic ecosystems and human populations.This study investigates the presence of microplastics (MPs) and heavy metal contamination in the Nida River in Poland. The research analyzed MPs, heavy metal concentrations, and physicochemical properties of water samples collected from five locations along the river. The results showed a wide range of MPs, including fibres, fragments, pellets, and foams, with an average of 245 ± 21 MPs per litre. The MPs varied in size, with an average size of 2852 ± 899 micrometers. The study also identified various heavy metals, with zinc having the highest average concentration at 96.86 ± 40.25 µg/L, followed by lead at 37.6 ± 31.9 µg/L. The water samples exhibited fluctuations in heavy metal levels, with pH, turbidity, and conductivity values also being measured. The health risk assessment indicated that the HQ and HI values for adults and children were below one, suggesting a low non-carcinogenic risk. However, the carcinogenic excess lifetime cancer risk (ELCR) exceeded the threshold value in most samples. The study highlights the importance of monitoring MPs and heavy metal contamination in freshwater sources to ensure water quality and human health. The findings emphasize the need for effective pollution management and water quality standards to protect aquatic ecosystems and human populations.