It is not uncommon to find waterbodies in India covered with a thick mat of vegetation. At times, the cover is so uniform that water birds mistake it for solid ground. This vegetation is water hyacinth (Eichhornia crassipes), one of the most invasive aquatic plants. A fast-growing floating species, it has a significant impact on lakes and waterbodies worldwide. The plant forms dense mats on the water’s surface, disrupting ecosystems and causing multiple ecological and economic problems.
Hyacinth mats obstruct sunlight from reaching submerged plants, which can lead to a reduction in dissolved oxygen levels, potentially harming aquatic life. The plant outcompetes native aquatic vegetation and disrupts habitats for fish, birds and other organisms. As dead hyacinths decay, they contribute to eutrophication, which can trigger algal blooms. This further depletes dissolved oxygen, reducing the ecological productivity of the aquatic ecosystem.
Hyacinth-covered lakes also have economic consequences. The dense mats hinder the movement of fishing boats, reduce fish catches and damage fishing gear. When hyacinths are drawn into water distribution systems, they clog pipes and disrupt water flow. Additionally, the stagnant, light-deprived water beneath these mats creates ideal breeding grounds for disease vectors such as mosquitoes.
Waterbodies across the world have struggled with hyacinth infestations. Simply removing the vegetation is rarely a long-term solution, as it quickly regrows. In Africa, hyacinth has spread extensively across Lake Victoria, threatening livelihoods, biodiversity and water access for local communities. In Zambia, its proliferation has disrupted hydropower operations and the fishing industry.
India has not been spared either. From Haryana’s Bhindawas lake to Kerala’s iconic Vembanad, water hyacinth has spread aggressively. In Indian cities, hyacinth-choked lakes impose a financial burden on cash-strapped municipal corporations. The Katraj and Pashan lakes in Pune, Pichhola Lake in Udaipur and Ulsooru Lake in Bangalore are among the affected waterbodies.
The Pune Municipal Corporation (PMC) spends significant sums on the periodic mechanical removal of hyacinths. In some cases, biological control methods using weevils (Neochetina spp.) and chemical treatments have been attempted, but their environmental impacts remain insufficiently studied.
The PMC is considering using glyphosate, a commercial herbicide, to control water hyacinth. This approach is seen as a potentially cheaper alternative, as the dead plants are easier to remove. Before proceeding with glyphosate application at Pashan Lake, the PMC sought an environmental impact assessment from a consortium of citizen groups and scientists from the CSIR-National Chemical Laboratory and the Indian Institute of Science Education and Research.
The agency advocating glyphosate use presented findings from a study conducted on a small farm plot. Their report claimed that glyphosate residue in the soil was negligible and posed no health risks. However, they provided no data on its effects on waterbodies, aquatic life, or long-term ecological consequences.
The Union Ministry of Environment, Forest and Climate Change has directed Maharashtra State Wetland Authority to address complaints raised by non-govenmental organisations regarding glyphosate use in Powai Lake. The Maharashtra Pollution Control Board granted the Brihanmumbai Municipal Corporation conditional approval for glyphosate application, contingent on measures such as stopping raw sewage entry, conducting bioaccumulation studies and submitting regular water and sediment analyses.
Despite a pilot project in 2022 that used drones for spraying, concerns persist over ecological risks, particularly in crocodile habitats and the need to address pollution sources rather than introducing chemical interventions.
Scientists at CSIR-NCL’s Biochemical Sciences Division proposed a rapid assessment of glyphosate’s effects using fruit flies (Drosophila spp.). This article discusses early findings from the study, along with a literature review. We argue that the use of glyphosate in public waterbodies should not proceed without comprehensive, long-term studies on its effects on aquatic flora and fauna.
Glyphosate is one of the most widely used herbicides globally, employed in agriculture, gardens and lawns to eliminate unwanted vegetation and boost crop yields. Since its introduction in 1974, glyphosate has been sold in more than 130 countries and used for weed control on over a hundred different crops.
It works by interfering with the shikimic acid pathway, which is an important precursor for synthesising essential aromatic amino acids in bacteria, plants and lower eukaryotes. Since this pathway is absent in animals, glyphosate is generally considered non-toxic to them.
However, glyphosate does impact other biological pathways relevant to both aquatic and terrestrial animals. Scientific studies have demonstrated its toxicity to various aquatic organisms, including fish, algae and invertebrates. Its potential role in the decline of amphibian and aquatic species has also been investigated. When in contact with water, glyphosate breaks down into aminomethylphosphonic acid (AMPA), which retains the toxic properties of its precursor.
Glyphosate can persist for extended periods in both soil and water, leading to potential accumulation in surrounding ecosystems. It binds to inorganic clays, organic compounds and sediments in freshwater environments, with an average half-life ranging from 12 days to 10 weeks. Following its application to control aquatic plants, glyphosate residues have been detected in surface waters for prolonged durations, posing risks to non-target species. For instance, its presence in soil can threaten microorganisms.
A small-scale laboratory study at CSIR-NCL examined the toxic effects of glyphosate on fruit flies, a well-established model organism for toxicology research. Our results indicate that the recommended commercial dosage of glyphosate formulation is highly toxic, leading to approximately 50-60 per cent mortality among flies that ingested it.
There are significant concerns about glyphosate accumulation in food, with potential implications for human health. Numerous scientific studies have linked glyphosate exposure to respiratory dysfunction, hypotension, metabolic disorders, neurological complications, kidney dysfunction, genotoxicity and adverse effects on gut microbiota. The International Agency for Research on Cancer has classified glyphosate as “probably carcinogenic” (Group 2A), citing evidence of its association with non-Hodgkin lymphoma.
On the other hand, a three-year randomised trial conducted in Karnal, Haryana, tested glyphosate alongside six other herbicides on water hyacinth. The study found that glyphosate was ineffective in controlling hyacinth, with the weeds regenerating after treatment. This further supports arguments against using glyphosate in waterbodies.
It is important to acknowledge the ongoing scientific debate regarding the extent of glyphosate’s environmental and health risks. However, the majority of evidence suggests that glyphosate is a hazardous substance that should be used with caution. Alternatives include both traditional methods and emerging biological herbicides, which are more sustainable and have no known detrimental effects on ecosystems.
Based on our review of research publications and reports on glyphosate use, as well as the preliminary findings of the CSIR-NCL study, we do not recommend the use of any herbicide to control water hyacinth. Furthermore, glyphosate-treated hyacinth does not reduce removal costs, as the dead plants must still be extracted from the water. Given the long-term and far-reaching ecological consequences, we argue that the precautionary principle should be applied, particularly when intervening in freshwater ecosystems.
Ashish Lele is director, CSIR-National Chemical Laboratory, Pune; Gurudas Nulkar is director, Centre for Sustainable Development, Gokhale Institute of Politics and Economics, Pune and Rakesh Joshi is scientist, Biochemical Sciences Division, CSIR-National Chemical Laboratory, Pune
Views expressed are the author’s own and don’t necessarily reflect those of Down To Earth