“Fish species such as mahseer and catfish, abundant in Dhansiri, require oxygen levels above 4-6 mg/L to survive. A BOD of 18.0 mg/L risks creating hypoxic zones, leading to fish kills, suffocation of benthic invertebrates, and disruption of the river’s food web,” he added.He added that the high COD level reflected a toxic mix of oxidisable pollutants from refinery processes, which could impair reproduction, stunt growth, and bioaccumulate in aquatic species, ultimately affecting predators such as birds and mammals.“The oil and grease content of 11.5 mg/L, though seemingly modest, forms a surface sheen that blocks oxygen exchange, coats fish gills, and smothers aquatic plants, further compounding the ecological stress,” he noted.Goswami urged the CPCB to conduct a detailed investigation into NRL’s effluent treatment practices and compliance with pollution control standards as of March 2025.He also called for a cumulative assessment of the discharge’s impact on Dhansiri’s aquatic life and water quality, long-term monitoring of oxygen levels and biodiversity, and stringent corrective measures to ensure BOD, COD, and oil and grease levels remain within permissible limits.
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