Arkavathi River pollution has reached alarming bacterial levels at Hesaraghatta Reservoir and downstream of Kanakapura town, according to September water-quality data released by the Karnataka State Pollution Control Board (KSPCB). Total coliform levels touched 1.4 lakh most probable number (MPN) per 100 ml at Hesaraghatta and 1.6 lakh MPN per 100 ml downstream of Kanakapura, while fecal coliform levels were recorded at 46,000 MPN and 8,400 MPN per 100 ml respectively.
The readings are substantially above the Central Pollution Control Board’s benchmark for a drinking water source after conventional treatment and disinfection. The CPCB standard sets the acceptable total coliform level at 5,000 MPN per 100 ml or below. The entire Arkavathi stretch covered by the monitoring exercise is classified as Class D, intended for the propagation of wildlife and fisheries under the CPCB’s designated-use criteria.
KSPCB monitors five locations on the river: Hesaraghatta Reservoir, Tippagondanahalli Reservoir, Manchanabele Reservoir, the river before its confluence at Sangam, and the stretch downstream of Kanakapura town. The results show that contamination is uneven rather than uniformly distributed across the river system.
At Manchanabele Reservoir, total coliform stood at 1,700 MPN per 100 ml and fecal coliform at 240 MPN per 100 ml. The readings were lower at the monitoring station before the river’s confluence at Sangam, where total coliform was 94 MPN per 100 ml and fecal coliform was 17 MPN per 100 ml. By comparison, Tippagondanahalli Reservoir recorded total coliform of 16,000 MPN per 100 ml and fecal coliform of 3,500 MPN per 100 ml.
The same monitoring data also recorded variations in dissolved oxygen (DO) and biochemical oxygen demand (BOD), two indicators used to assess the condition of water bodies. At Tippagondanahalli, DO was 4.8 milligrams per litre and BOD was 7 milligrams per litre. Hesaraghatta recorded DO of 6.7 milligrams per litre and BOD of 4 milligrams per litre, while Manchanabele recorded DO of 5 milligrams per litre and BOD of 5 milligrams per litre. Downstream of Kanakapura, DO stood at 5.4 milligrams per litre and BOD at 7 milligrams per litre.
Experts cited in the report linked the contamination to untreated sewage and waste entering the river from settlements along its course. Nirmala Gowda of Mapping Malnad said the Vrishabhavathi, which drains Bengaluru, joins the Arkavathi carrying organic and inorganic waste. She also attributed part of the pollution load to sewage from Ramanagara, Kanakapura and parts of Bengaluru.
Gowda said direct waste discharge from Doddaballapura town was a concern at Hesaraghatta. She added that sewage treatment plants (STPs) exist in the affected areas, but Ramanagara and Kanakapura do not have complete sewerage networks and their STPs are not operating at designed capacity. The gap between treatment infrastructure and the sewer connections needed to feed it remains a central issue in the reported contamination.
The Arkavathi is therefore being monitored as part of a wider state water-quality programme rather than as an isolated local waterway. Under the Central government’s National Water Monitoring Programme, the KSPCB tracks water quality in 12 rivers across Karnataka, including the Arkavathi, Cauvery, Kabini, Krishna, Tungabhadra, Bhadra, Tunga and Netravati. The latest readings identify Hesaraghatta and the downstream Kanakapura stretch as the locations requiring the closest attention in the reported monitoring cycle.
