In a recent report, the Central Pollution Control Board (CPCB) has termed the Cooum river in Chennai the "most polluted" river in the country.

According to the report, Biomedical Oxygen Demand (BOD) in the river between Avadi to Sathya Nagar was 345 mg per litre, the highest among the 603 rivers of the country.

Interestingly, the Sabarmati river in Gujarat, with a BOD of 292 mg per litre and Bahela in Uttar Pradesh, with a BOD value of 287 mg per litre, are the second and third most polluted rivers, respectively.

The report also states that the number of polluted rivers in Tamil Nadu has increased in the past four years. The CPCB report titled, 'Polluted River Stretches for Restoration of Water Quality, 2022' states that the water quality of 12 rivers in Tamil Nadu was monitored at 73 locations during the period between 2019 to 2021.

The report said that Biomedical Oxygen Demand (BOD) in 53 locations of 10 rivers did not comply with the prescribed water quality criteria.

The ten rivers are Adyar, Amaravati, Bhavani, Cauvery, Cooum, Palar, Sarabanga, Tamaraibarani, Vasishta and Tirumanimuthar in Tamil Nadu.

Notably, Tamaraibarani and Cooum rivers have been highly polluted for the past few years, with environmentalists and social workers relentlessly campaigning against the unabated pollution.

Even as the Cooum river has become the highly polluted river in the country, steps have been taken by the present government to clean it.

Almost 80% of encroachments along the river banks have been removed, and three treatment plants have been set up at Langs Garden in Egmore, Nungambakkam and Chetpet. The authorities are now focusing on preventing the flow of untreated sewage into it.

The treatment plants will biologically treat the polluted water, followed by sedimentation and filtration to enhance its quality. After that, it is chlorinated for disinfection and is ready for non-potable purposes like gardening.