New Delhi, Aug 7 : As many as 311 polluted river stretches (PRS) have been identified on 279 rivers by Central Pollution Control Board (CPCB), the Lok Sabha was informed on Thursday.

The stretches were identified based on monitoring results in terms of Bio-Chemical Oxygen Demand (BOD), as an indicator of organic pollution.

Minister of Jal Shakti C.R. Paatil, in a written reply, said the number of PRSs has decreased from 351 identified in the year 2018 to 311 in the year 2022 across 30 States/Union Territories.

As many as 106 PRSs have been delisted, and improvement in water quality of 74 polluted river stretches has been observed in 2022 as compared to the report published in 2018, the Minister said in response to questions by Bhausaheb Rajaram Wakchaure and Bharti Pardhi.

Minister Paatil added that the CPCB initiated the exercise of identifying PRSs in 2009 based on the river water quality monitored during the past years on a periodic basis.

"So far, CPCB has published four such periodic reports in 2009, 2015, 2018 and 2022," said the Minister.

Asked about the extent to which the existing water quality monitoring mechanisms including real-time monitoring stations and manual sampling have proved effective, the Minister said, "The existing water quality monitoring mechanisms, comprising both manual sampling under the National Water Quality Monitoring Programme (NWMP) and Real-Time Water Quality Monitoring Stations (RTWQMS) have played a significant role in tracking and managing river water pollution across the country."

The CPCB at present monitors water quality of aquatic resources at 4,736 locations across the country, which includes 2,155 locations on 645 rivers, he said.

He said that as per the CPCB, water quality data is obtained from the manual water quality monitoring carried out under NWMP, and it is utilised for the identification of PRS.

These stations help in assessing the polluted river stretches and preparation of action plans for these stretches, he said.

Highlighting the steps to strengthen the surveillance network and ensure accuracy and transparency of data, the Minister said, "Water samples are analysed for Surface water and groundwater parameters as per Guidelines for Water Quality Monitoring, 2017, issued by the Ministry of Environment, Forest and Climate Change."

Water samples are tested in National Accreditation Board for Testing and Calibration Laboratories (NABL) accredited labs to ensure accuracy, and auditing of monitoring locations under NWMP is annually carried out by CPCB through its Regional Directorates, he said.

State Board laboratories participate in the Analytical Quality Control (AQC) carried out by CPCB for proficiency testing, followed by posting of water quality data on the CPCB website, he said.

/IANS