Overview The Cauvery River, a vital water source in South India, is increasingly threatened by pollution from various sources. Its tributaries now function more like drains, and the river is used to absorb untreated sewage and industrial waste. This contamination impacts agriculture, public health, and the overall ecosystem. Key Pollution Sources Industrial Effluents: Discharge from dyeing, bleaching, and tannery units. Untreated Sewage: Domestic waste from cities and towns along the river. Agricultural Runoff: Fertilizers and pesticides entering the river. Pharmaceutical Residues: Emerging contaminants affecting water quality. Regional Hotspots Mettur At Mettur Dam , industrial effluents are allegedly discharged during flood season when surplus water is released. M. Thangaraj , president of the Tamil Nadu Iyarkkai Vivasayigal Munnetra Sangam , claims this is done deliberately to dilute the waste and avoid detection. Dead fish are often found near the banks, attributed to low dissolved oxygen levels caused by the effluents. Erode Erode is a major urban pressure point. A 17-kilometre stretch within the Erode Corporation limits is heavily contaminated. The city generates 35 to 40 million litres of sewage daily, with only about 8 MLD treated. The Central Pollution Control Board (CPCB) classified this stretch as polluted in 2022 . Namakkal In Namakkal district, dyeing units that relocated from Tiruppur contribute to pollution. A. Adhavan alleges that these units illegally pump Cauvery water and discharge untreated effluents back into the river. Residents are forced to buy packaged water due to fears of pollution and potential health risks. Karur In Karur , farmers' protests and a court ruling led dyeing units to adopt zero liquid discharge (ZLD) systems. However, domestic sewage and industrial waste continue to flow unchecked. Effluents stored at the Orathupalayam dam are now discharged downstream, entering the Cauvery at Semangi . Impact of Encroachments Traditional safeguards like neer nilai porambokku (waterbody commons) and vella karai porambokku (flood-bank commons) that historically prevented construction and industry along the river's edge have been dismantled, exacerbating the crisis. UPSC Relevance This issue is highly relevant to GS3: Environment, Conservation, and Pollution . It highlights the challenges of balancing industrial development with environmental sustainability. Understanding the sources and impacts of river pollution is crucial for Mains answers on environmental governance and sustainable development. Key Terms for UPSC Effluent: Liquid waste discharged into a water body. Tributary: A stream or river that flows into a larger river. Sewage Treatment Plant (STP): Facility for treating wastewater. Zero Liquid Discharge (ZLD): Industrial wastewater treatment process. TNPCB: Tamil Nadu Pollution Control Board. CPCB: Central Pollution Control Board.