The Cooum River originates in a village of the same name in
Kadambathur union in Tiruvallur district, about from Chennai, although starting its main course at Sattarai village, around from Chennai. Flowing through
Thiruverkadu, it enters the
Chennai District at
Arumbakkam after meandering for about . It then passes through some of the oldest residential areas for another such as
Choolaimedu,
Chetpet,
Egmore and
Chintadripet, where the river channel is about wide. Close to Egmore, the river forks into two—the northern and the southern arms—both of which join again near the
Napier bridge, thus forming an island, known as the Island Grounds. The northern part of the
Buckingham Canal joins the Cooum near the old Central Jail while the southern part of the same canal emerges from the river, just behind the
University of Madras campus. The river finally joins the
Bay of Bengal south of the
Fort St George, just below the Napier Bridge. Once a fresh water source, it is today a drainage course inside the city of Chennai. The total length of the river is about . The river flows to a length of in the Chennai Metropolitan Area, of which fall within the Chennai district limits. The total catchment area of the river is about , and the bed width ranges from . The capacity of the river is , and the anticipated flood discharge is around . Once a fishing river, it has borne the brunt of the city's unplanned developmental explosion. The Kesavaram dam diverts the river into the
Chembarambakkam Lake from which water is used for the supply of drinking water to the city of Chennai. Thereafter, the flow of water in the river is much reduced. Three ancient
Shiva temples are located at the source of the river. The first is
Tiruvirkolam, in Cooum village, and the other is at Ilambaiyankottur. The third is Thiruverkadu Shiva temple. Koyambedu temple is also in its banks. These temples have been featured in the
Thevaram sung by the
Saivite saint
Thirugnana Sambandar. There is one more temple called the Veerebathrasami temple. The god in the temple is otherwise known as "Akoramoorthy". This temple is at Pillayarkuppam, from Cooum village. In ancient Tamil Nadu, under the Chola Empire, the river Cooum was referred to as
Kashtabudhyotpathihi. They all form a group of villages called
Padhinaru Nattham. The river drains into the Bay of Bengal at
Chepauk in Chennai marking the northernmost boundary of the
Marina Beach. The delta also marks the southern boundary of the
Port of Chennai. The width of the river course varies all along from , which includes the area occupied by the slums. ==Islets and the river mouth==