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Fish kill in Ashtamudi Lake
Context
A large number of dead fish were found floating on Ashtamudi Lake in Kollam, Kerala. This event attracted attention due to the suspected causes and its environmental implications.The lake, covering 5,700 hectares, is an ecologically important site recognized by the Ramsar Convention.
Factors Responsible for Killing Fish in Ashtamudi Lake
- Algal Bloom: Algal bloom occurs when there is an overload of nutrients (especially nitrogen and phosphorus) in the water. These nutrients primarily come from pollution, particularly untreated sewage and agricultural runoff.
- Algal blooms deplete oxygen in the water, suffocating fish and other aquatic life. This causes widespread mortality of aquatic organisms.
- Sewage Contamination: The lake has been heavily polluted by untreated sewage from nearby households and establishments. A significant percentage of sewage is directly discharged into the lake, increasing the nutrient load and contributing to algal blooms.
- The presence of harmful bacteria like E. coli and streptococci in water samples confirms contamination from human and animal waste.
- Plastic Pollution: A high concentration of microplastics has been found in the water, fish, and sediment of Ashtamudi Lake. Plastics pose direct threats to aquatic organisms by causing physical harm and introducing toxins into the ecosystem.
- Plastic waste comes from various sources, including fishing activities, aquaculture, and municipal solid waste dumping.
- Other Pollutants: Along with plastics, the lake is contaminated by abattoir waste, poultry waste, and chemicals from various industrial and agricultural activities. These pollutants further degrade water quality and disrupt the aquatic ecosystem.
- Sediment Build-up: Sedimentation in the lake, especially from poor waste management practices, reduces water flow, affecting oxygen levels and overall water quality. This contributes to the degradation of habitats for aquatic species.
- Invasive Species: The spread of water hyacinth, an invasive aquatic plant, is also limiting fishing areas. It blocks the flow of water and interferes with fishing practices, adding to the challenges faced by local fishermen.
- Deforestation and Encroachments: Illegal encroachments and deforestation around the lake’s fringes have further disrupted its ecosystem. Encroachments restrict natural water flow and contribute to pollution.
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