KOCHI: Kerala’s rivers are gradually losing their health due to urbanisation and relentless discharge of untreated sewage, according to the latest assessment by the Central Pollution Control Board (CPCB). The findings, contained in the CPCB’s report ‘Polluted River Stretches for Restoration of Water Quality – 2025’, are based on water quality data collected during 2022 and 2023.
The assessment is based on Biochemical Oxygen Demand (BOD), the primary indicator used to evaluate river water quality. BOD measures the amount of dissolved oxygen required by microorganisms to break down organic matter in water. In simple terms, the higher the BOD, the greater the organic pollution and the poorer the water quality.
Overall, Kerala accounts for 32 polluted river stretches and monitoring locations—the second highest in the country after Maharashtra.
However, unlike heavily industrialised states, Kerala has no rivers in the two most severe pollution categories. Instead, 26 of its 32 polluted stretches fall under Priority Class V, the lowest pollution category.
“The rivers are generally healthy in their upper reaches and deteriorate rapidly once they pass through urban centres,” said Linto Alappat of the department of geology and environmental science, Christ College, Irinjalakuda.
“Our rivers are not dying because they lack water; they are dying because they have become carriers of untreated sewage,” he said.
Rapid urbanisation, he pointed out, has far outpaced Kerala’s sanitation infrastructure, while rivers continue to be treated as drainage channels rather than living ecosystems.
Further, Linto said that waste from lakhs of septic tanks and household drains seeps into streams every day, untreated. Sand mining and the filling of paddy fields have made it worse, leaving rivers too shallow to flush themselves clean for much of the year.
Kerala’s river water quality tells a mixed story. While India’s overall polluted river stretches fell from 351 in 2018 to 296 in 2025, Kerala moved against this national trend, with its count rising to 32 stretches in 2025 — making it one of only twelve states where pollution levels increased.
Encouragingly, most previously flagged stretches actually improved: nine dropped off the polluted list entirely and four shifted to less severe categories, while only one deteriorated. The rise is driven almost entirely by 19 newly identified polluted stretches uncovered through expanded monitoring, rather than worsening of known rivers.
Experts said the state’s biggest challenge is the near absence of underground sewerage networks. A study, ‘Water Quality Degradation in Kerala: The Challenge Ahead’, by Srikumar Chattopadhya, notes that urban stretches of Kerala’s rivers have increasingly exhibited the “urban river syndrome”, having lost much of their ecological function. CPCB data analysed in the study highlighted that nearly half of the water samples tested in the state were bacteriologically contaminated, while rising nutrient loads and coliform levels contributed to a more than 35% increase in water-borne diseases between 2012 and 2016.
Environmentalists argue that every urban local body should be mandated to establish sewage treatment plants within fixed timelines, backed by decentralised treatment systems wherever conventional sewer networks are impractical.
“Recharging groundwater, restoring flow and reviving river ecosystems are not merely environmental goals. They are tourism policy. A visitor who sees a filthy backwater or falls ill from the water, does not come back—and tells others not to bother,” Alappat said.
“Kerala has the rainfall, the local bodies and the public awareness to run the cleanest rivers in India. What it has not yet done is treat a dying river as an emergency,” he added.