The correct option is A Mahanadi River
The Gangrel Dam, also known as the R.S. Sagar Dam, is built across the Mahanadi River in Dhamtari district of Chhattisgarh. It is the longest dam in Chhattisgarh. This dam supplies year round irrigation, allowing farmers to harvest two crops per year. The dam also supplies 10 MW of hydro-electric power capacity.