Yamuna water quality improved in Delhi in August compared with July, but pollution levels remained well above prescribed limits at several monitoring points, with biochemical oxygen demand (BOD) reaching 28 milligrams per litre at the ISBT bridge, according to the latest Delhi Pollution Control Committee (DPCC) data.
The DPCC monitors water quality at seven locations along the river: Palla, Wazirabad, the ISBT bridge, the ITO bridge, the Nizamuddin bridge, the Okhla barrage and Asgarpur, also known as Kidwali, in Haryana. Samples are tested for BOD, dissolved oxygen, chemical oxygen demand, pH and faecal coliform, among other parameters.
Faecal coliform levels fell significantly at all six major Delhi locations in August. However, five sites recorded levels above the maximum acceptable limit of 2,500 MPN per 100 millilitres. Palla and Wazirabad were the only locations where the levels remained within that limit, according to the report.
The desired faecal coliform level for river water is 500 MPN per 100 millilitres. The continued exceedance at five monitoring points indicates that the improvement during August did not bring water quality within the preferred or acceptable range across most of the monitored stretch.
BOD levels also improved compared with July but remained elevated at several locations. The August readings ranged from 3 to 28 milligrams per litre, against a prescribed maximum of 3 milligrams per litre. The highest reading was recorded at the ISBT bridge, where BOD was 28 milligrams per litre.
BOD measures the amount of oxygen required by microorganisms to break down organic matter in water. Higher levels indicate a greater organic pollution load and can reduce the oxygen available for aquatic life. The readings at several points therefore show that the river continues to face substantial biological pollution despite the month-on-month improvement.
The DPCC report attributed the decline in faecal coliform levels partly to a possible reduction in untreated sewage entering the river. Rainfall may also have contributed by diluting pollutants and temporarily improving water-quality readings during the monsoon period. Such dilution, however, does not by itself indicate that the underlying sources of pollution have been eliminated.
The data on drains points to that continuing challenge. Wastewater from several drains that discharge directly into the Yamuna, as well as subsidiary drains connected to the Najafgarh drain, recorded high BOD and total suspended solids levels in August. These readings indicate that the drains remain a significant source of pollution entering the river.
The latest figures therefore show two contrasting conditions: a short-term improvement in some water-quality indicators and continued failure to meet standards at multiple locations. The DPCC’s monitoring programme covers the principal points required to track changes along the Delhi stretch, while drain-quality readings indicate that untreated or inadequately treated wastewater remains central to the river’s pollution burden.
The August data also places attention on the difference between river monitoring and pollution control. Improved readings at some locations provide evidence of a change during the month, but the high BOD at ISBT and faecal coliform levels above the acceptable limit at five sites show that the improvement was incomplete. Further monitoring will determine whether the change continues beyond the rainfall period.
