The influent and effluent characteristics of river Ganga in the Hardwar-Narora sector in Uttar Pradesh, India was studied using environmental oxygen-18. delta-O-18 of river water and also of groundwater close to the river course was monitored at 8 stations along the 220 km stretch for a period of ten months. delta-O-18 of the river during the monsoon months (June to September) was about -10 at all the stations. However, during the dry months from October to April, the delta-O-18 of the river was enriched progressively from Hardwar to Narora. The enrichment indicated groundwater contribution to the river during the non-monsoon months. The contribution was comuted using the principle of isotope balance.
