This study investigates the presence of microplastics (MPs) and heavy metals in the Nida River in Poland. The river was found to contain various colored MPs, including fibers, fragments, pellets, and foams, with an average concentration of 245 ± 21 MPs per liter. The most common heavy metals were zinc (96.86 ± 40.25 μg/L) and lead (37.6 ± 31.9 μg/L). The study also assessed water quality parameters such as turbidity, pH, and conductivity, which were found to be outside recommended ranges. Health risk assessments revealed that while non-carcinogenic risks were low, carcinogenic risks exceeded threshold values in most water samples. The research highlights the need for continuous monitoring and management strategies to protect freshwater ecosystems and human health.This study investigates the presence of microplastics (MPs) and heavy metals in the Nida River in Poland. The river was found to contain various colored MPs, including fibers, fragments, pellets, and foams, with an average concentration of 245 ± 21 MPs per liter. The most common heavy metals were zinc (96.86 ± 40.25 μg/L) and lead (37.6 ± 31.9 μg/L). The study also assessed water quality parameters such as turbidity, pH, and conductivity, which were found to be outside recommended ranges. Health risk assessments revealed that while non-carcinogenic risks were low, carcinogenic risks exceeded threshold values in most water samples. The research highlights the need for continuous monitoring and management strategies to protect freshwater ecosystems and human health.