Maharashtra, Assam, Gujarat account for 117 sections

The number of polluted stretches of the country's rivers has increased to 351 from 302 two years ago, and the number of critically polluted stretches — where water quality indicators are the poorest — has gone up to 45 from 34, according to an assessment by the Central Pollution Control Board (CPCB).

While the ₹20,000 crore clean-up of the Ganga may be the most visible of the government’s efforts to tackle pollution, the CPCB says several of the river’s stretches — in Bihar and Uttar Pradesh — are actually far less polluted than many rivers in Maharashtra, Assam and Gujarat. These three States account for 117 of the 351 polluted river stretches.

Based on the recommendations of the National Green Tribunal, the CPCB last month apprised the States of the extent of pollution in their rivers.

Mithi among the worst

The most significant stretches of pollution highlighted by the CPCB assessment (which is yet to be published) include the Mithi river — from Powai to Dharavi — with a BOD (Biochemical Oxygen Demand) of 250 mg/l; the Godavari — from Someshwar to Rahed — with a BOD of 5.0-80 mg/l; the Sabarmati — Kheroj to Vautha — with a BOD of 4.0-147 mg/l; and the Hindon — Saharanpur to Ghaziabad — with a BOD of 48-120 mg/l.

In its compilation of polluted stretches in Uttar Pradesh, the Ganga, with a BOD range of 3.5-8.8 mg/l is indicated as a ‘priority 4’ river.

“The cultural significance of the Ganga is such that there’s been greater focus on it but many more rivers are far more polluted,” said an officer in the Union Water Resources Ministry, who didn’t want to be identified.

Graded scale

The CPCB, since the 1990s, has a programme to monitor the quality of rivers primarily by measuring BOD, which is a proxy for organic pollution — the higher it is, the worse the river. The health of a river and the efficacy of water treatment measures by the States and municipal bodies are classified depending on BOD, with a BOD greater than or equal to 30 mg/l termed ‘priority 1,’ while that between 3.1-6 mg/l is ‘priority 5.’

The CPCB considers a BOD less than 3 mg/l an indicator of a healthy river.

In its 2015 report, the CPCB identified 302 polluted stretches on 275 rivers, spanning 28 States and six Union Territories.

A person involved in the monitoring exercise, who didn’t wish to be identified as he was not authorised to speak to the media, told The Hindu that the increase in numbers reflected higher pollution levels as well as an increase in water quality monitoring stations.

“We have used about 500 more monitoring stations in our 2016-2017 assessment than for the previous exercise (2008-2012). A priority 1 river may show high pollution but it also means more resources for clean up, whereas a priority 4 can mean achieving a clear river with relatively fewer resources,” he said.

Based on its 2008-2012 evaluation, the CPCB published a report in 2015 and asked the States to prepare plans for improving these polluted stretches. Though the information from the 2016-2017 assessment doesn’t indicate improvements, the bulk of the increase in polluted stretches were in priority 4 (6-10 mg/l) and priority 5 river stretches

Currently, the CPCB has 1822 monitoring stations on rivers and 473 on lakes/ponds/tanks.