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The Polluted River Stretches (PRS) assessment by the Central Pollution Control Board (CPCB) provides a national snapshot of river health using a statutory, Biological Oxygen Demand (BOD)-based criterion. This page traces the timeline of PRS assessments, with a particular focus on Karnataka’s rivers, including those in the Cauvery basin.
The Primary Water Quality Criteria for Bathing Waters Gazette Notification (2000) was issued by the Ministry of Environment and Forests under the Environment (Protection) Act, 1986. It specified that surface waters with Biological Oxygen Demand (BOD) levels above 3 mg/L are classified as polluted. This enforceable statutory threshold subsequently became the basis for national assessments of organic pollution in rivers
Based on river water quality data collected between 2002 and 2008, the Central Pollution Control Board (CPCB) in its 2009 report identified 150 polluted river stretches (PRS) across India.
Within Karnataka, the CPCB identified eight polluted river stretches across eight rivers: Bhadra, Tunga, Tungabhadra, Malaprabha, Kali, Krishna, Arkavathi, Lakshmantirtha.
Of these eight, two—Arkavathi, Lakshmantirtha—are part of the Cauvery basin
Based on river water quality data collected between 2009 and 2012, the Central Pollution Control Board (CPCB) in its 2015 report identified 302 polluted river stretches (PRS) across 275 rivers in India. Compared to 2009, the number of polluted river stretches rose sharply from 150 to 275, indicating a significant nationwide deterioration in river water quality
Within Karnataka, the CPCB identified 15 polluted stretches across 15 rivers: Arkavathi, Bhima, Bhadra, Cauvery, Ghataprabha, Kagina, Kabini, Kali, Krishna, Lakshmantirtha, Malaprabha, Manjira, Shimsha, Tunga, Tungabhadra
Of these fifteen, five – Cauvery, Arkavathi, Kabini, Lakshmantirtha, Shimsha – are in the Cauvery Basin
Based on river water quality data collected between 2009 and 2012, CPCB in its 2018 report identified 351 polluted river stretches across 323 rivers in India.
Within Karnataka, the CPCB identified 17 polluted stretches: Asangi, Arkavathi, Bhima, Bhadra, Cauvery, Kagina, Kabini, Kali, Krishna, Kumardhara, Lakshmantirtha, Malaprabha, Netravathi, Shimsha, Tunga, Tungabhadra, Yagachi
Of these seventeen, six – Cauvery, Arkavathi, Kabini, Lakshmantirtha, Shimsha, Yagachi – are in the Cauvery Basin
The National Green Tribunal (NGT) took suo moto cognisance of the worsening state of rivers in India based on a news item dated 17 September 2018, titled “More river stretches are now critically polluted: CPCB”, registered as Original Application No. 673/2018.
It observed that the large number of polluted river stretches revealed a failure by several State Pollution Control Boards (SPCBs) to fulfil their statutory obligations under the Water (Prevention and Control of Pollution) Act, 1974. Consequently, the Tribunal directed all States and Union Territories to prepare and submit time-bound action plans for the restoration of the identified polluted river stretches.
Following this intervention, numerous sewage-treatment infrastructure projects were commissioned across the country.
Based on water quality data collected in 2019 and 2021 (excluding the COVID year 2020), the CPCB in its 2022 report identified 311 polluted river stretches across 279 rivers.
Within Karnataka, the CPCB identified 17 polluted stretches across 17 rivers — the same number as in the 2018 assessment. However, the composition of the list changed: five rivers were removed, and five new ones were added.
Removed: Yagachi, Asangi Nalla, Kali, Malaprabha, and Kumardhara
Added: Aghanashini, Dakshina Pinakini, Gangavali, Thenpennai, and Sharavathi
So the 17 polluted river stretches of Karnataka: Aghanashini, Arkavathi, Bhima, Bhadra, Cauvery, Dakshina Pinakini, Gangavali, Kagina, Kabini, Krishna, Lakshmantirtha, Netravathi, Sharavathi, Shimsha, Thenpennai, Tunga, Tungabhadra,
Of these seventeen, five – Cauvery, Arkavathi, Kabini, Lakshmantirtha, Shimsha – are in the Cauvery Basin.
Based on water quality data collected in 2022 and 2023, the CPCB in its 2025 report identified 296 polluted river stretches across 271 rivers. This marks a slight improvement from the 2022 assessment, which recorded 311 polluted stretches, yet the overall picture remains one of widespread degradation.
Within Karnataka, the CPCB identified 14 polluted stretches. However, the composition of the list changed.
Four rivers were removed, and two were added or re-added.
Removed: Aghanashini, Gangavali, Netravathi, and Sharavathi
Added: Malaprabha and Ghataprabha
So the 14 polluted river stretches of Karnataka: Arkavathi, Bhima, Bhadra, Cauvery, Dakshina Pinakini, Ghataprabha Kagina, Kabini, Krishna, Lakshmantirtha, Malaprabha,Shimsha, Tunga, Tungabhadra,
Of these fourteen, five – Cauvery, Arkavathi, Kabini, Lakshmantirtha, Shimsha – are in the Cauvery Basin.
Although the number of polluted river stretches remained unchanged, both the severity of pollution and the length of the polluted stretches increased
