This study presents a comprehensive analysis of arsenic contamination in the Tigris River, Iraq, with a focus on seasonal variations and their relationship with water quality parameters. Conducted from November 2022 to July 2023, this research involved quarterly sampling at ten stations along the river and its tributaries. Arsenic levels were measured using a Shimadzu AA-6300 atomic absorption device, and water quality parameters such as dissolved oxygen (DO), total hardness, total dissolved solids (TDS), electrical conductivity (EC), and pH were assessed. This study revealed significant seasonal fluctuations in arsenic concentrations, with the highest levels detected during the winter season. Eight out of ten stations exceeded the World Health Organization's guideline limit of 10 µg L-1 for arsenic in drinking water during winter, with concentrations at the more contaminated stations reaching up to 16 times this limit. The research found no significant correlation between arsenic concentration and the water quality parameters measured, suggesting that these parameters are not reliable predictors of arsenic contamination. The highest arsenic concentrations were consistently observed at the first three stations, indicating a localized source of contamination likely due to the dissolution of arsenic from arsenic-rich soil layers. This study also noted the potential for bioremediation, as evidenced by the reduced arsenic levels at station 4 during the winter, which correlated with the presence of arsenic-absorbing Chara algae. The findings highlight the urgent need for targeted remediation efforts to mitigate arsenic pollution and protect public health in the region. پرونده مقاله