river, Tamil Nadu (Tamil Nādu) state, southeastern India. Formed by the northern bifurcation of the Kaveri (Cauvery) River (Kaveri River) at Srirangam, the Coleroon River flows between the South Arcot and Thanjavur regions for 36 miles (58 km) and empties through several mouths into the Bay of Bengal (Bengal, Bay of) 3 miles (5 km) south of Porto Novo. The Coleroon is part of the Kaveri delta, the most fertile and densely populated region of southern India, noted for its rice production. The town of Chidambaram lies on its banks.