The CPCB tracks rivers health in two-year cycles, focusing particularly on Biological Oxygen Demand (BOD) as a key indicator.

• BOD represents the amount of oxygen consumed by bacteria and other microorganisms while they decompose organic matter under aerobic (oxygen is present) conditions at a specified temperature.

Criteria for deciding PRS

• The locations/ stretches of rivers where BOD levels exceed 3 mg/L, failing to meet the primary water quality standard for outdoor bathing, are classified as polluted stretches or polluted locations.
• PRS are categorized under five Priority Classes (I to V) on the basis of maximum BOD level observed. 
  • BOD of Priority I and V is more than 30.0 mg/ L and 3.0 – 6.0 mg/ L, respectively. 

Key Findings: 

• In 2023, monitoring recorded 296 polluted river stretches (PRS) across 271 rivers, compared to 311 PRS across 279 rivers in 2022.
• Maharashtra (54) had the maximum number of PRS or locations followed by Kerala (31).
• The number of ‘Priority 1’ stretches reduced to 37 from 45 over the 2022 assessment. 
  • Tamil Nadu, Uttar Pradesh and Uttarakhand had the maximum number of stretches or locations in ‘Priority I’.