The present study evaluates the physico-chemical parameters of the Vaigai River at five sampling sites during August 2015 and August 2025 to understand spatial and temporal variations in water quality. Parameters including pH, electrical conductivity, total dissolved solids (TDS), alkalinity, hardness, calcium, magnesium, iron, chloride, nitrate, phosphate, fluoride, Dissolved oxygen (DO), Biological oxygen demand (BOD) and Chemical oxygen demand (COD) were analysed. Results revealed that pH remained largely neutral to mildly alkaline across most sites, although a decline was noted at the downstream station (S5) in 2025, reflecting localized pollution inputs. Conductivity decreased in 2025 compared to 2015, while TDS showed a sharp rise, particularly at Kochadai (S5), indicating increasing contamination from domestic, agricultural and industrial discharges. Hardness and associated ions (Ca, Mg, Fe) were elevated at downstream sites, confirming high anthropogenic influences. Nutrients such as nitrate and phosphate exceeded acceptable limits in several locations, highlighting risks of eutrophication and nitrate-related health concerns. Fluoride concentrations also increased in 2025, surpassing permissible levels at multiple sites. Organic pollution indicators showed marked temporal changes: in 2015, DO levels were critically low (0.9–1.5 mg/L) and BOD extremely high (24–32 mg/L), reflecting severe organic loading; by 2025, DO improved substantially (4.3–9.6 mg/L), while BOD decreased (4.5–22.5 mg/L) but remained above safe levels in downstream stretches. The comparative analysis demonstrates partial improvement in water quality over the decade, yet persistent organic and nutrient pollution continues to affect downstream reaches. Overall, the findings indicate that while the Vaigai River exhibits some recovery, sustained anthropogenic pressures necessitate enhanced wastewater treatment, stricter pollution control and continuous monitoring to restore ecological balance and ensure water safety.
