The Cooum River originates from the surplus course of Cooum tank in Tiruvallur District. It runs east for a distance of about 65 kilometres and confluences with the Bay of Bengal downstream of Napier Bridge, traversing a distance of 20 kilometres within Chennai city limits.
Cooum River Sub-Basin is a narrow drainage basin of about 505.88 Sq.km situated between the Kosasthalaiyar sub-basin on the northern side and Palar basin and Adyar basin on the southern side. Cooum River is fed by Kosasthalaiyar river surplus from Kesavaram Anicut through old Bangaru channel and Palar river surplus from Palar anicut through Govindavadi Channel, Kambakkal Channel and the chain of surplus courses of groups of tanks. Cooum River also supplies water to Chembarambakkam lake in the Adyar Sub-basin from Korattur Anicut through New Bangaru Channel. Cooum River is connected to its adjoining basins through the Buckingham Canal. Cooum River supports a substantial portion of irrigation and additional rain fed agriculture in its upper part and also provides water supply to Chennai city and its adjoining areas. Cooum River also acts as the major flood carrier for Chennai city with its arms viz., Otteri Nallah in the north (10.8 km) and Virugambakkam to Arumbakkam drain in the south (6.4 km).

The upper catchment of Cooum River is primarily rural and as it enters the peri-urban areas and Chennai City, the river is constrained in channels before draining into the Bay of Bengal. The Cooum River in its upstream rural areas shows issues of catchment degradation and tank siltation. There is also no minimum flow maintained in the river during the lean season. As the river flows through peri-urban areas and municipalities, there are increasing problems of water quality. The highly polluted reputation of the river also leads to public apathy and disposal of solid waste on the river bed that impacts downstream water quality and oxygen levels in the water. When it enters the city, the river is basically an urban sewer receiving municipal and industrial wastewater and solid waste (especially near bridges) and refuse from slums. This results in the direct impact of polluted anoxic stretches, as well as raises public health (including from mosquito breeding in stagnant waters) and odour concerns and secondary groundwater pollution. The river mouth is subject to blockage by sand bars resulting from littoral drift creating a lack of tidal exchange in the river.

The Project area presently being covered for restoration comprises the stretch from Paruthipattu to the river mouth in the Bay of Bengal. It was proposed to take up the restoration from Paruthipattu as the major sources of pollution have been observed to be downstream of Paruthipattu, in the densely populated urban areas.

The eco-restoration of Cooum River is being carried out with the following objectives:

• To ensure effective abatement of pollution and protection of rivers by adopting a sustainable approach to promoting inter-sectoral co-ordination through comprehensive planning and management.
• To maintain ecological flows into the river with the aim of ensuring water quality and sustainable development.
• To develop the river front within urbanized areas, wherever possible.
• To explore potential future uses of the river after restoration.

The implementation of the eco-restoration project is being carried out by various Line Departments as detailed below: