The Himachal Pradesh State Pollution Control Board (HPSPCB) has confirmed that the fish mortality incident reported in the Ratti rivulet of Mandi district on June 12 was caused by the discharge of untreated effluent and sewage into the water body, leading to a sharp decline in water quality and depletion of dissolved oxygen levels.
The findings emerged after laboratory analysis of water samples collected from different locations along the rivulet on June 12 and June 13. According to Vinay Kumar, Regional Officer of HPSPCB, Mandi, the test results revealed alarming levels of pollution in the downstream stretch of the stream, clearly indicating contamination from untreated sewage and organic waste.
The board subsequently shared the findings with the General Manager of the District Industries Centre (DIC), Mandi, after issuing show-cause notices under the Water (Prevention and Control of Pollution) Act, 1974, and the Environment (Protection) Act, 1986.
The analysis highlighted a stark contrast between the quality of water upstream and downstream of the affected site. Samples collected downstream recorded significantly higher levels of biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS) and coliform bacteria, all of which are indicators of severe pollution.
On June 12, the downstream sample showed a BOD level of 70 mg/l and coliform counts exceeding 1,600 MPN per 100 ml. Meanwhile, a sample collected from a discharge chamber connected to the industrial area recorded an extremely acidic pH value of 3.82, TSS of 164 mg/l, and an exceptionally high COD level of 4,400 mg/l.
HPSPCB officials said the presence of untreated sewage and organic pollutants in the stream resulted in oxygen depletion, creating conditions unsuitable for aquatic life and ultimately causing the fish deaths reported by local residents.
Following the notices issued by the board, the District Industries Centre informed HPSPCB that immediate corrective measures had been undertaken. These included repairing the soak pit, removing accumulated sludge, cleaning chambers and preventing further discharge of untreated wastewater into the rivulet.
The DIC has also informed the board that long-term solutions are being explored, including upgrading the existing infrastructure into a full-fledged Sewage Treatment Plant (STP) or relocating the facility to a more suitable site.
A follow-up inspection conducted by HPSPCB on June 19 found no active discharge entering the Ratti rivulet from the identified source. Fresh water samples were collected from the downstream stretch to assess the current status of water quality. The board has directed authorities to ensure strict compliance with pollution control norms and has stated that regular inspections and monitoring of effluent disposal will continue to prevent recurrence of such incidents.
