Why is Weed Infestation at Mumbai’s Powai Lake a Problem?

Mumbai’s Powai Lake is just another water body that has witnessed multiple clean-up drives over the years. However, its problems remain unchanged, with a long-running weed infestation across the 210-hectare lake.

Powai Lake is surrounded by several prominent institutions—from IIT Bombay on one side to corporate spaces and high-end residential infrastructure on the other—while also being home to legally protected crocodiles. The weed infestation has, for some time now, been far more complex than water hyacinth alone, involving multiple invasive species, as recently confirmed by the ICAR, according to our sources.

In November last year, the civic body, the Brihanmumbai Municipal Corporation, launched a Rs. 66-crore restoration project at Powai Lake. This includes diverting existing sewage lines, setting up a modern sewage treatment plant, and accelerating efforts to remove the extensive spread of water hyacinth that has long been choking the lake’s surface.

However, the infestation is not limited to water hyacinth alone and has added further layers of complexity. According to Dr. Archana Anokhe, a scientist at ICAR’s Directorate of Weed Research and a Fellow of the Entomological Society of India, the infestation “appears to involve a complex of invasive aquatic weeds, with Alternanthera suspected to be a dominant component, interspersed with water hyacinth in certain zones.”

The scientist, who is also a visiting scholar at Israel’s Agricultural Research Organisation, made these observations after assessing photographs, conducting field visits, and reviewing inputs shared by environmental watchdog NatConnect Foundation.

The organisation’s director, B N Kumar, had earlier approached Dr. J S Mishra, Director of ICAR’s Directorate of Weed Research in Jabalpur, seeking scientific intervention as the weed problem persisted despite repeated clean-up drives over the years. Following this, Dr. Mishra asked Dr. Anokhe to examine the issue, including images showing a dense green carpet choking large sections of the lake.

Floating problems of the lake

Reportedly, Powai Lake, an artificial lake in Mumbai, was built by the British in 1891. Its purpose was to dam the Mithi River and supply drinking water to the growing city, and it was named after the Framaji Kavasji Powai Estate.

While it remained important initially, pollution from urban growth rendered the water unfit for drinking by the 1930s, shifting its use to non-potable purposes and recreational activities under the Maharashtra State Angling Association.

Now an ecological spot, Powai Lake has seen a sharp increase in water hyacinth in recent months, caused by untreated sewage acting as a nutrient source. Calling the situation “shameful”, the NGO’s director states that an estimated 18 million litres of untreated sewage continue to flow into Powai Lake every day through 19 inlets, worsening the weed infestation.

“The nutrient-rich sewage acts as a continuous fertiliser for invasive plants, undermining clean-up efforts and explaining why repeated mechanical harvesting has failed to deliver lasting results,” she adds.

The lake assumes added significance as one of Mumbai’s major wetlands, identified in the National Wetland Atlas published by the Union Ministry of Environment, Forest and Climate Change.

Responding to photographs, Dr. Anokhe notes that the problems cannot be addressed through routine mechanical removal alone, while also emphasising that her observations are preliminary and limited by the absence of on-ground verification.

NatConnect has, therefore, formally requested the Brihanmumbai Municipal Corporation (BMC), through Commissioner Bhushan Gagrani, to facilitate the proposed study in the larger public interest. The communication has also been marked to the Chief Minister of the state.

Dr. Anokhe explained that such mixed infestations require species-specific, science-led interventions rather than uniform mechanical measures. ICAR has also highlighted the need for structured field trials to identify effective management options and expressed its willingness to visit Mumbai for on-site verification and studies, subject to logistical facilitation.

In her detailed response, Dr. Anokhe outlined species-specific scenarios: “Water hyacinth (Eichhornia crassipes) is present at the site, for which ICAR can supply a limited quantity of the biological control insect Neochetina spp. Salvinia (Salvinia molesta), another invasive floating fern, has established management options. However, Alternanthera spp., believed to be a major component of the infestation, poses the biggest challenge,” she says.

With scientific support now seemingly on the table, environmentalists are emphasising that the civic body must look beyond costly, repetitive mechanical harvesting and adopt long-term, science-based solutions. Echoing this concern, Pamela Cheema, chairperson of a BMC-mandated Advanced Locality Management (ALM) group, said ICAR’s involvement “offers hope that Mumbai can finally move towards a lasting, evidence-based solution.”

Citing international precedents, NatConnect notes that globally tested programmes exist for Alternanthera philoxeroides (alligator weed), including research by Australia’s CSIRO, the Queensland Government, the USDA Agricultural Research Service, and CABI’s Invasive Species Compendium.

“A sustainable solution is essential for Powai Lake,” Kumar adds, noting that unchecked weed cover blocks sunlight, depletes dissolved oxygen, and threatens biodiversity, including fish populations and the lake’s crocodiles.

On the matter, B N Kumar recalls that a National Green Tribunal (NGT)-mandated committee has already recommended stringent penalties against the BMC should it fail to curb pollution entering Powai Lake. The NGT’s Western Zonal Bench is scheduled to hear the case on 12 February.