Data shows ‘zero oxygen’ stretches in Sal, sewage and waste choking lifeline

Margao: Even as water resources minister Subhash Shirodkar has ordered a systematic clean-up and restoration of the Sal river, hard data and ground-level inspections have laid bare the alarming decline of the river, with parts of it recording zero oxygen levels, widespread sewage discharge, and unchecked dumping of fish waste.

Following an inspection last week, Shirodkar directed officials to act urgently, stressing that stopping direct sewage inflow must be a priority. Calling the Sal the “lifeline of Salcete”, he said restoring it would require both administrative action and public participation.However, official water quality data for 2025 tabled in the House in the recently concluded assembly session tells a far more troubling story.

In the river’s lower stretches, dissolved oxygen (DO) — essential for aquatic life — dropped to below detectable levels for five consecutive months at one monitoring point. The Central Pollution Control Board norm for rivers designated for drinking water use with treatment requires a minimum of 6mg/l.

Experts said such readings indicate a near-total collapse of aquatic conditions, typically caused by heavy inflow of untreated sewage and decomposing organic waste.

Biochemical oxygen demand (BOD), another key pollution indicator, remained above safe limits during this period, peaking at 6 mg/l, suggesting sustained organic pollution overwhelming the river’s natural capacity to recover.Ground inspections by the Goa State Pollution Control Board (GSPCB) back the data. At the SGPDA wholesale fish market, Margao, untreated wastewater from trucks and fish-handling areas was found flowing directly into storm water drains connected to the river.Trucks were seen discharging waste with valves left open, while fish remains, plastic, and thermocol boxes littered nearby areas.The market’s proximity to the river raises the risk of direct contamination.Multiple sewage leak points have compounded the crisis. Near South Goa District Hospital, an overflowing manhole was found spilling sewage into surrounding fields, accompanied by foul odours and reports of dead fish.In Fatorda, signs of recent sewage discharge into a freshwater nullah — including sludge deposits and discoloured water — point to ongoing contamination.Farmers say polluted water is entering agricultural lands, raising concerns over crop safety.Water clarity has also deteriorated, with turbidity levels touching 79.7NTU, nearly three times the permissible limit. While monsoon flows temporarily dilute pollution, they also bring silt and runoff.

In the dry months, reduced flow concentrates pollutants, worsening the crisis.But not all stretches are equally affected. Midstream areas such as Panzorconi remain relatively stable, while downstream zones show severe degradation, indicating localised pollution sources.The GSPCB has observed that despite earlier directives to install and maintain effluent treatment systems and halt illegal discharge, compliance has remained poor across several inspections.It has called for immediate corrective action, urging the proper functioning of effluent treatment systems, strict enforcement against illegal waste disposal, and regular clearance of fish and solid waste at the SGPDA market. The Margao Municipal Council and other planning authorities have been asked to take ownership of drainage and sewage management failures identified during the inspections.Experts warn that without swift, coordinated enforcement, the ecological damage to the Sal risks becoming irreversible.