“Though industrial waste has reduced since the lockdown, the pollution level in the river will come down only when medical wastes discharged from the hospitals are controlled. Majority of hospitals are situated around the Cooum; so it is obviously more polluted than other city rivers,” said a senior PWD official on condition of anonymity.

Industrial waste is discharged into the river till Maduravoyal. But beyond Koyambedu, the major pollutant is the medical waste from hospitals, including Rajiv Gandhi Government General Hospital, Government Kilpauk Medical College Hospital and Government Stanley Medical College Hospital, allege activists.

Though the Chennai Metropolitan Water Supply and Sewerage Board (Metro Water) is setting up sewage treatment plants (STP), it is being used only to treat domestic sewage. “But they should be set up even for hospitals. Only then the waste will be controlled,” the PWD official added. In contrast, the pollution level at Adyar has reduced by an estimated 40 per cent because the main source of pollution there are the industries that have remained shut for the last two months, said another official. “It is not as polluted as Cooum, as there are less than 10 per cent healthcare centers near Adyar compared to Cooum,” the official added.

However, the problem of domestic sewage still persists, which, the official said, would be addressed after the work on setting up STPs is completed once the lockdown is lifted.

Last week, the PWD sent samples of water from Adyar to Tamil Nadu Pollution Control Board for testing, and are awaiting results, the person added.

On the other hand, the city lakes are in a better condition, as the toxic waste from industries has reduced considerably. “We sent samples from the lakes, which showed improvement by 30 – 40 per cent in the last two months. The groundwater extraction for industries has also come down,” said G Radhakrishnan, Assistant Executive Engineer, Water Resources Department (WRD).