 The dam is located in Kerala on the river Periyar, but is operated and maintained by the neighbouring state of Tamil Nadu.Although the Periyar River has a total catchment area of 5398 km2 with 114 km2 downstream from the dam in Tamil Nadu, the catchment area of the Mullaperiyar Dam itself lies entirely in Kerala and thus not an inter-State river.However, by the principle of estoppel it is considered otherwise.