Mullaperiyaru Dam is a masonry gravity dam on the Periyar River in the Indian state of Kerala It is located above mean sea level, on the Cardamom Hills of the Western Ghats in Thekkady, Idukki District of Kerala, South India. It was constructed between 1887 and 1895 by John Pennycuick and also reached in an agreement to divert water eastwards to the Madras Presidency area (present-day Tamil Nadu). It has a height of from the foundation, and a length of . The Periyar National Park in Thekkady is located around the dam's reservoir. The dam is built at the confluence of Mullayar and Periyar rivers. 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. On 21 November 2014, the water level hit 142 feet for first time in 35 years. The reservoir again hit the maximum limit of 142 feet on 15 August 2018, following incessant rains in the state of Kerala.