Toxic drain water flows into DPS flamingo lake in Navi Mumbai, raises STP quality questions

Navi Mumbai: A fresh laboratory analysis of water drawn from the drain adjoining the DPS Flamingo Lake in Nerul in Navi Mumbai has raised serious environmental concerns with activists alleging that inadequately treated municipal discharge flows into the ecologically sensitive wetland during low tide.

The test found a pH of 9.12, indicating highly alkaline water that can disturb aquatic life and wetland ecology.

The sample, tested by SSAS Laboratory, showed a pH of 9.12 (against the acceptable 6.5–8.5 range), Total Dissolved Solids (TDS) at 7,950 mg/L (against the prescribed maximum of 2,100 mg/L), and Biochemical Oxygen Demand (BOD) at 36.4 mg/L (above the permissible 30 mg/L limit).

Chemical Oxygen Demand (COD) was reported at 114.8 mg/L.

The laboratory concluded that the sample did not conform to inland water quality norms.

Environmental group NatConnect Foundation, which commissioned the test, said the findings raise questions about the quality of sewage treatment before discharge into the open drain that flows toward the wetland and onward to Thane Creek.

The high pH level indicates strongly alkaline water that can disturb aquatic life, affect microorganisms and worsen stress in fragile wetland ecosystems. Elevated TDS points to excessive salts and dissolved pollutants, while high BOD suggests organic contamination that can reduce oxygen available for fish and other aquatic species.

“This is not a routine storm-water channel. It carries water that reaches the flamingo wetland during low tide. If such quality is entering the system, serious questions arise on treatment standards and monitoring,” said B N Kumar, Director of NatConnect.

The latest findings come amid continuing concern over the health of the DPS Flamingo Lake, part of the wider wetland chain linked to the Thane Creek Flamingo Sanctuary.

Earlier water quality examinations of the DPS lake itself had indicated heavy organic loading, algal growth and signs consistent with sewage intrusion. Independent assessments had recorded elevated BOD, alkaline stress and high dissolved solids, while field observations noted froth, oily traces and thick algae mats on the water surface.

Experts quoted by activists had earlier warned that such indicators often suggest inflow of urban wastewater or mixed sewage discharge, making the habitat unsuitable for aquatic organisms that sustain flamingos and other migratory birds.

NatConnect said the new drain sample strengthens the need for an independent audit of the civic sewage treatment plant and its filtration standards, especially as the same outflow is believed to move toward the creek ecosystem.

“The issue is larger than one lake. If partially treated water is flowing through drains into wetlands and the creek, the ecological cost could be significant,” Kumar said.

Rekha Sankhala of Save Mangroves & Flamingos Forum called for real-time monitoring of STP output, tidal-flow studies, plugging of illegal sewage entry points and restoration of the DPS wetland before the next migratory bird season.

The activists have also been experiencing a terrible stink at the lake.