Periyar, IPA: [peɾijɐːr], is the longest river and the river with the largest discharge potential in the Indian state of Kerala. It is one of the few perennial rivers in the region and provides drinking water for several major towns. The Periyar is of utmost significance to the economy of Kerala. It generates a significant proportion of Kerala's electrical power via the Idukki Dam and flows along a region of industrial and commercial activity. The river also provides water for irrigation and domestic use throughout its course besides supporting a rich fishery. Due to these reasons, the river has been named the "Lifeline of Kerala". Kochi city, in the vicinity of the river mouth, draws its water supply from Aluva, an upstream site sufficiently free of seawater intrusion. Twenty five percent of Kerala's industries are along the banks of the Periyar. These are mostly crowded within a stretch of 5 kilometres (3 mi) in the Eloor-Edayar region (Udhyogamandal), about 10 kilometres (6 mi) north of Kochi harbor.

The Idukki Dam is a double-curvature arch dam constructed across the Periyar River in a narrow gorge between two granite hills locally known as Kuravan and Kurathi in Idukki district in the state of Kerala, India. It is constructed and owned by the Kerala State Electricity Board. It supports a 780 MW hydroelectric power station in Moolamattom, which started generating power on 4 October 1975. At 168.91 metres (554.2 ft), it is one of the highest arch dams in Asia. The Indo-Canadian project was inaugurated by the Prime Minister Indira Gandhi on February 17, 1976.