A growing number of lakes, ponds and urban water tanks in India are turning red, raising alarm among scientists and residents alike. These striking red algal blooms, caused by euglenophytes, are not just unusual sights but indicators of ecological stress. Experts warn that they thrive in polluted, nutrient-rich waters and can severely harm aquatic ecosystems and communities dependent on them.
Why Waters Are Turning Red
Unlike the more familiar green algal mats, these blooms get their crimson colour from a pigment called astaxanthin, produced by certain euglenoids. Organisms like Euglena, Phacus and Trachelomonas flourish in oxygen-poor, stagnant waters enriched by sewage discharge, agricultural runoff and industrial effluents. Their adaptability being able to photosynthesise like plants and feed like animals allows them to dominate stressed water bodies, especially during warm months.
A Threat to Aquatic Life and Communities
The ecological impacts are serious. Euglenoid blooms deplete oxygen at night, leading to sudden drops in oxygen levels that suffocate fish and other organisms. Thick scums on the surface block sunlight, disrupting plant growth and upsetting the ecological balance. In some cases, toxins such as euglenophycin stick to fish gills or directly kill aquatic life. The result is frequent fish deaths, biodiversity loss and disruptions in aquaculture systems.
For urban residents, these blooms also diminish the cultural and recreational value of lakes and temple tanks, while creating foul odours and murky water. Water utilities face added costs, as blooms clog filters and complicate treatment. In aquaculture farms, the consequences translate into economic losses, with reduced fish growth and health.
Indian Cities at the Centre of the Crisis
In India’s urban and peri-urban landscapes, red algal blooms are becoming common warning signs of deteriorating water quality. Already stressed by population growth and poor waste management, city water bodies are hotspots for such outbreaks. Their presence signals untreated sewage inflows, organic pollution and collapsing aquatic ecosystems.
Scientists argue that despite the growing prevalence of these blooms, euglenophytes remain poorly studied. Little is known about their toxin levels, seasonal patterns or precise responses to environmental changes such as pH and temperature. Without this understanding, effective monitoring and management remain difficult.
Urgent Call for Action
Environmental experts describe red-coloured water as a biological red flag a visible warning that ecosystems are collapsing under pressure from urbanisation and neglect. Addressing the crisis requires strict sewage management, better monitoring of algal communities and ecosystem-based restoration measures.
Researchers also stress the need to revive ecological studies and microscopic analysis in universities to close knowledge gaps. Without such detailed assessments, policymakers cannot accurately gauge the risks these organisms pose. Stronger environmental regulations, combined with citizen participation, could help protect India freshwater bodies from further decline.