CHENNAI: The central government has confirmed that Thenpennai river, flowing from Karnataka into Tamil Nadu, is severely polluted due to unchecked discharge of industrial effluents and untreated sewage from Bengaluru’s sprawling urban and industrial zones.
In a written reply to a question from DMK MP TR Baalu in the Lok Sabha on Monday, Minister of State for Environment, Forest and Climate Change Kirti Vardhan Singh admitted the downstream stretches of rivers like the Thenpennai are heavily contaminated.
The ministry’s statement corroborated findings by Tamil Nadu authorities and national monitoring agencies that identified the river at Chokkarasanapalli Bridge in Karnataka – near Tamil Nadu border – as a Priority-I polluted river stretch, the most critical category under national classification.
Water quality data collected under the National Water Quality Monitoring Programme revealed alarming figures: Biochemical oxygen demand (BOD) levels at Chokkarasanapalli ranged between 17 and 52.4 mg/L, far exceeding the safe threshold of 3 mg/L.
Even more concerning was the total coliform levels – an indicator of fecal contamination – peaking between 16 lakh and 350 lakh MPN/100 ML, alongside dangerously low dissolved oxygen levels.
The Central Pollution Control Board (CPCB) reported that in some cases, dissolved oxygen is below detectable limits.
These findings mirror the findings in a recent report by the Tamil Nadu Water Resources Department (WRD) submitted to the southern bench of the National Green Tribunal (NGT). The WRD had flagged that untreated effluents from Bengaluru were flowing downstream via the heavily polluted Bellandur, Agara, and Varthur lakes, crossing into Tamil Nadu through Sokkarasanapalli in Krishnagiri district and accumulating in the Kelavarapalli Reservoir. WRD officials noted discolouration of the river water along with the smell of sewage and no signs of aquatic life.
The impact is far-reaching. Over 9,000 acres of farmland irrigated by the Kelavarapalli and Krishnagiri dams has been affected, and drinking water sources for Hosur and nearby towns are at risk, said D Shanmuganathan, standing counsel for Tamil Nadu government in the NGT, during the last hearing.
While Karnataka has promised to build new sewage treatment plants, TN officials have criticised the lack of interim measures to curb pollution. The centre noted that CPCB has directed Karnataka authorities to take corrective steps, but enforcement and progress remain slow.