Background: Microplastic (MP) contamination in freshwater systems has emerged as a critical global environmental threat, yet spatiotemporal dynamics in major South Asian river basins remain poorly quantified. The Ganges River, supporting over 400 million people, faces intense anthropogenic pressure, but seasonal variability in MP loads is not well understood.

Objective: This study aims to quantify the abundance, morphological characteristics, and polymer composition of MPs in surface waters of the lower Ganges basin across monsoon and dry seasons, and to assess associated ecological risks using the Polymer Hazard Index (PHI).

Method: Surface water samples were collected from 12 strategic sites along a 300-km stretch during peak monsoon (August 2024) and dry season (February 2025). Samples were processed via vacuum filtration (0.45 µm), digested with 30% H₂O₂, and analyzed using stereomicroscopy and Fourier Transform Infrared Spectroscopy (FTIR). Ecological risk was evaluated using PHI and Potential Ecological Risk Index (PERI).

Key Results: Mean MP abundance was significantly higher in the dry season (8.4 ± 2.1 items/m³) compared to the monsoon season (3.2 ± 1.4 items/m³). Fibers dominated morphology (68%), and polyethylene (PE) and polypropylene (PP) constituted 72% of identified polymers. PHI values indicated "High" to "Very High" hazard levels at urban-adjacent sites during both seasons.