Coordinates: 13°00′49″N 80°15′56″E / 13.01367°N 80.26559°E / 13.01367; 80.26559 Adyar (Tamil: அடையார்) or Adayar, originating near the Chembarambakkam Lake in Chengalpattu district, is one of the two rivers which winds through Chennai (Madras), South India, and joins the Bay of Bengal at the Adyar Estuary. The 42.5 km-long river contributes to the estuarine ecosystem of Chennai. Despite the high pollution levels, boating and fishing take place in this river. The river takes in surplus water from about 50 tanks and lakes, small streams and the rainwater drains in the city. Most of the waste from the city is drained into this river and the Cooum.

Adyar river starts from Malaipattu tank (80.00° latitude and 12.93° longitude) near Manimangalam village in Sriperumbudur Taluk at about 15 km west of Tambaram near Chennai. It starts to appear as a stream only from the point where water from Chembarambakkam lake joins the river. It flows through Kancheepuram, Tiruvallur and Chennai district for about 42.5 km before joining the Bay of Bengal in Adyar, Chennai. Here it forms an estuary, which extends from the Adyar Bridge to the sandbar at the edge of the sea, with some small islets in-between. The estuary covering an area of about 300 acres was made a protected wildlife reserve in 1987.

Maraimalai Adigal (Tamil: மறைமலை அடிகள்) (15 July 1876 – 15 September 1950) was an eminent Tamil orator and writer. He was a devout Hindu as a staunch follower of Saivism. He has authored more than 100 books, including works on original poems and dramas, but most famous are his books on his research into Tamil literature. Most of his literary works were on Saivism. He founded a Saivite institution called Podhunilaik Kazhagam. He was an exponent of the Pure Tamil movement and hence considered to be the father of Tamil puritanism. He advocated the use of Tamil devoid of Sanskrit words and hence changed his birth name Vedhachalam to Maraimalai.

Politically he was inclined towards non-Brahminism and hence he and his followers considered that the Self-respect movement was born out of his efforts. Nevertheless, the atheist ideologies of Periyar E. V. Ramasamy were shunned by Maraimalai Adigal and caused years of differences between the two. Maraimalai Adigal spent most of his income on buying his books and after his death his collection were made into a library according to his will.