This study provides a comprehensive assessment of the Ganga River’s ecological condition at the Sangam, Prayagraj, during the Maha Kumbh, 2025, integrating water quality dynamics and microplastic contamination across pre-, during-, and post-event phases. Physicochemical parameters showed notable temporal variation. Before the event, the river exhibited good quality with high dissolved oxygen (10.2–10.7 mg/L) and low BOD (2.1–2.6 mg/L). During the event, deterioration occurred with increased BOD (up to 8.8 mg/L), COD (up to 30 mg/L), and nutrient enrichment (nitrate: 3.1 mg/L; phosphate: 0.52 mg/L; sulphate: 35.5 mg/L) from mass bathing and ritual discharges. Post-event recovery was partial, with BOD and nutrients remaining elevated. Correlation analysis revealed strong positive links among BOD, COD, and sulphate (r = 0.80–0.93) and a negative correlation between DO and organic loads (r = –0.58 to –0.75). Microplastic abundance increased from 60–153 particles before the event to 80–311 during and 99–495 after, with mean concentrations rising from 22.07 ± 9.39 to 70.0 ± 43.60 particles/L. FTIR confirmed dominant polymers polyethylene terephthalate (PET), polystyrene (PS), polyamide (Nylon), polycarbonate (PC), high-density polyethylene (HDPE), and acrylonitrile–butadiene–styrene (ABS), indicating mixed domestic and industrial sources. SEM imaging revealed irregular, cracked, and pitted fragments typical of secondary, weathered plastics, while EDS analysis detected elements such as O, Si, Zn, Ba, and Nb, suggesting mineral deposition and metal adsorption on polymer surfaces. The Maha Kumbh acted as a temporary pollution pulse, intensifying organic, nutrient, and microplastic loads. Effective waste management, reduced plastic usage, and continuous monitoring are crucial to preserve the ecological integrity of the Ganga River.
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