The mainstream of Gandak river is the boundary between India and Nepal near the Valmiki Tiger Reserve (VTR) on the western side. The government of India constructed a barrage in 1964 and also planned to construct guide bundhs on both sides of the river to save the bank from erosion. While a guide bundh has been constructed on the Nepal side, the Bihar government failed to do that. Since then, more than 2,500 hectares of forest land have been washed away by the river.

In this process, a big island has been formed within the Indian territory of the river belt called Susta. "The change in mainstream is still taking place towards the Madanpur forest area in the VTR and several lakh trees have been swept away by the river over the years, besides destroying wildlife habitat,' says Ashok Prasad, conservator of forests.