Ganga river supports about 500 million population in the Gangetic Plain. Still, the occurrence of toxic pollutants in the Ganga river is an emerging concern, questioning its ecological health. This study is the first to quantify the microplastic (MP) and its characteristics, seasonal dynamics (pre-monsoon and post-monsoon), and environmental risk in the 19 sites (sample size, n = 228) in the upper Himalayan stretch of Ganga (Devprayag, Zone-I
Rishikesh, Zone-II
Haridwar, Zone-III) with multiples sampling (6 months). Average MP particles were found in the range of 100-1550 particles/L in water and 50-1300 particles/kg in sediment samples. MP flux showed an increased trend (Zone-I <
Zone-II <
Zone-III) while the river flows from the foothills of the Himalayas to densely populated bank cities. MP-sized 500 μm to 5 mm were dominant in sediment (45.68 %) and water (52.73 %) during pre-monsoon. MP-sized 500 μm to 5 mm, 250 μm to 500 μm, and 50 μm to 250 μm were found to be 45.68 %, 27.57 %, and 26.75 % in water and 52.73 %, 23.03 %, and 24.24 % in sediments, respectively with abundance during post-monsoon. μATR-FTIR analysis revealed polyethylene, polyamides and polystyrene as dominant polymers and no drastic change occurred in polymer types between studied seasons. The fibers were the predominant particle type, followed by fragments and films across the studied stretch of the Ganga river. The pollution load index suggested that Zone-I and Zone-II fall under hazard category 1 while Zone-III in category 2. Polymer hazard index and potential ecological risk index data suggested an extreme pollution level of MP in a studied stretch of the Ganga river. This study emphasizes the adverse impacts of beach activities, tourist accommodations, and open waste disposals on river health, highlighting the urgent action required for effective plastic waste management. We urged a comprehensive study on MPs in the Ganga river basin, which serves as pathways and sinks for these particles into the ocean.