The latest evidence on Arkavathy River pollution shows that Bengaluru’s water crisis is not confined to the city’s municipal boundary. A Karnataka State Pollution Control Board report has recorded total coliform levels of up to 1,70,000 MPN/100 ml along the river stretch from Hesaraghatta Reservoir to Kanakapura, while experts point to untreated sewage, faecal contamination, agricultural runoff, damaged riverbank vegetation and weak monitoring as connected parts of the problem.
The figure is 34 times the Central Pollution Control Board’s Class C criterion of 5,000 MPN/100 ml or less. It is not simply a measure of dirty water. It is an indication of how multiple urban and rural systems are discharging into a shared river basin without being adequately tracked or managed as one system.
The Arkavathy was once a lifeline for Bengaluru. Today, the stretch from Hesaraghatta Reservoir to Kanakapura is classified under Priority I, the CPCB’s highest pollution category for polluted river stretches based on biochemical oxygen demand. Madhuri Mandava of the Paani Earth Foundation said the CPCB recorded a maximum BOD of 72 mg/L at Hesaraghatta during 2022–23, well above the Priority I threshold of more than 30 mg/L.
Together, the coliform and BOD readings describe different aspects of the same failure. Total coliform levels indicate faecal and organic contamination, while BOD reflects the amount of oxygen-consuming organic matter in the water. High BOD can reduce the oxygen available for aquatic life and is commonly associated with untreated or inadequately treated organic waste. The supplied evidence does not establish one single source for the contamination, but it does show that the pollution burden is spread across a river system receiving inputs from several settlements and land uses.
That distinction matters for restoration planning. If pollution is treated only at a visible point on the river, contamination entering from upstream towns, peri-urban settlements, industrial areas, farms or informal settlements may continue to undermine the river’s recovery. Mandava said reviews of restoration plans and progress reports showed gaps relating to sewage and faecal sludge from peri-urban towns and Gram Panchayats, sewage from industrial areas, gaps in common effluent treatment plant infrastructure and informal settlements that may fall outside sewerage plans.
This creates an institutional problem as much as an engineering one. Urban sewerage plans are generally organised around municipal jurisdictions, while rivers move across administrative boundaries. A town or Gram Panchayat may manage its own sanitation assets, industries may fall under separate regulatory arrangements, and agricultural land may not be covered by the same pollution-control framework. The river, however, receives the combined effect of all these activities.
The Arkavathy’s pollution therefore exposes the limits of treating sewage infrastructure as a city-only service. A treatment plant can work within its designed capacity and still fail to protect a river if neighbouring settlements have no connected sewerage network, if faecal sludge is not safely managed, or if industrial discharges are not consistently monitored. The report’s findings suggest that the relevant unit for planning is the full river stretch and its catchment, not only the jurisdiction where a discharge becomes visible.
Dr TV Ramachandra of the Centre for Ecological Sciences at the Indian Institute of Science attributed the deterioration to poor planning and inadequate sewage treatment. He said several towns were contributing sewage to the river and pointed to the low-cost treatment system at Jakkur as a model that could have been adopted to prevent sewage from entering the river.
The reference to Jakkur is significant because it shifts the discussion away from a single technology or a single large project. The available evidence does not provide a comparative performance assessment of treatment options, but it does raise a practical question: whether decentralised or lower-cost systems can be deployed in locations that are not served by large, centralised sewerage networks. For peri-urban settlements and smaller towns, the gap may not be the absence of any treatment technology but the absence of a functioning system that covers collection, treatment, maintenance and monitoring.
The same issue applies to faecal sludge. Where households and settlements are not connected to underground sewers, sanitation depends on containment, scheduled emptying, transport and treatment. Mandava’s reference to faecal sludge from peri-urban towns and Gram Panchayats indicates that the river’s pollution load may include waste flows that remain outside conventional sewerage planning. Without regular tracking of these flows, authorities may know that a river is polluted without knowing which pathways are contributing most to the contamination.
Agricultural runoff adds another layer. Experts cited in the report identify fertilisers carried by runoff as a major source of non-point pollution. Unlike a pipe discharging at a clearly identifiable location, runoff can enter waterways from many fields and drainage paths, particularly during rainfall. This makes it harder to assign responsibility and harder to address through conventional inspections alone.
The condition of the riverbank is part of this process. Dr Ramachandra said the loss of riparian vegetation had removed a natural barrier that can intercept runoff before it reaches the water. Vegetation along riverbanks can also slow the movement of contaminants and help stabilise the edge of the river. Its loss does not explain the entire pollution burden, but it reduces the landscape’s ability to filter some of the material moving towards the river.
This is why river restoration cannot be reduced to desilting, beautification or construction along the water’s edge. The supplied evidence points to a wider restoration agenda involving sewage collection, treatment capacity, industrial infrastructure, faecal-sludge management, agricultural runoff, riverbank vegetation and monitoring. If any of these elements is excluded, restoration reports may record activity without demonstrating a reduction in the pollution entering the river.
Monitoring is the point at which the system can either become accountable or remain descriptive. Dr Ramachandra said identifying pollution hotspots was not enough and called for regular monitoring to trace sources and guide mitigation. A hotspot map can show where water quality is poor, but it does not by itself establish whether the cause is a sewage outfall, an industrial discharge, runoff from farmland, a failing treatment facility or multiple sources operating together.
For governance, the distinction between measuring pollution and managing pollution is crucial. A periodic sample can document a serious condition. Repeated sampling at the same locations, combined with source tracing and records of corrective action, can show whether interventions are working. The report supplied for this story does not establish whether such a continuous source-tracking system is currently in place across the Arkavathy stretch.
The numbers also show why the problem cannot be treated as a minor water-quality fluctuation. A maximum BOD of 72 mg/L at Hesaraghatta during 2022–23 was more than twice the threshold associated with the CPCB’s Priority I category, while total coliform levels have now been reported at 1,70,000 MPN/100 ml. These measurements come from different indicators and periods, so they should not be combined into a single trend line. They do, however, demonstrate the scale of stress recorded in the river system.
The larger urban question is whether Bengaluru’s infrastructure planning recognises the ecological systems on which the city depends. Hesaraghatta and the Arkavathy are not only environmental assets; they are part of the region’s water geography. Pollution generated across a chain of settlements can weaken that system even when the sources are outside the core city and even when responsibility is divided among multiple agencies.
The evidence confirms that Arkavathy River pollution is being driven by more than one failure. It shows severe contamination, inadequate sewage treatment, agricultural runoff, loss of riparian vegetation and gaps in regular monitoring. What remains unclear from the available material is the precise contribution of each source and the implementation status of the restoration measures already reported. The next meaningful test will be whether authorities move from documenting polluted stretches to identifying, monitoring and reducing the specific pathways through which contaminants enter the river.