The Suffocation of Our Waters
The phenomenon is called deoxygenation, or hypoxia when oxygen levels are low and anoxia when they are absent entirely. Just like humans, aquatic organisms like fish, crabs, and countless microorganisms need oxygen to breathe. When the dissolved oxygen in
water drops below a critical threshold, it triggers a cascade of negative effects. Organisms that can move, like fish, flee the area. Those that cannot, like shellfish and corals, effectively suffocate and die. These events can lead to massive fish kills and turn vibrant ecosystems into barren underwater deserts, often called 'dead zones'. This isn't a new or entirely natural process; human activity has dramatically accelerated its spread and intensity since the mid-20th century.
A Crisis Driven by Two Key Factors
The loss of aquatic oxygen is primarily driven by two human-led forces: nutrient pollution and climate change. The first culprit is eutrophication, which happens when excessive nutrients like nitrogen and phosphorus from agricultural fertiliser runoff, untreated sewage, and industrial waste flood our water systems. These nutrients act like a super-fertiliser for algae, causing massive blooms. When these short-lived algae die, they sink and are decomposed by bacteria in a process that consumes huge amounts of oxygen. The second driver is global warming. Basic physics dictates that warmer water simply cannot hold as much dissolved oxygen as colder water. As global temperatures rise, the surface layers of oceans and lakes heat up, reducing their overall oxygen-carrying capacity. This warming also increases stratification, creating a stronger barrier between the oxygen-rich surface and the deeper, oxygen-poor layers, effectively cutting off the oxygen supply to the depths.
From Global Oceans to India's Lakes
This is a global crisis, with the total volume of ocean waters completely depleted of oxygen having quadrupled since the 1960s. But this is not a distant problem. In India, the effects are being felt in iconic water bodies and crucial coastal areas. Over 70% of India's surface water is considered polluted, creating fertile ground for deoxygenation. Lakes like Dal Lake in Srinagar, Hussain Sagar in Hyderabad, and Bellandur in Bengaluru have all suffered from severe eutrophication driven by sewage and nutrient overload, leading to oxygen depletion and ecological damage. The Bay of Bengal and parts of the Arabian Sea are also recognised as having large, naturally occurring low-oxygen zones, which are now being intensified by climate change and coastal pollution, threatening marine life along India's vast coastline.
The Ripple Effect on Life and Livelihoods
The consequences of deoxygenation ripple through entire ecosystems and human societies. For India's millions of fishermen, it means smaller catches or total collapse of local fisheries as fish populations are either killed or forced to migrate. This directly impacts food security and economic stability for coastal and lakeside communities. The loss of biodiversity is another major concern, as sensitive species disappear and are replaced by a few tolerant, often less desirable ones, simplifying complex food webs. Furthermore, low-oxygen conditions can alter the water's chemistry, potentially releasing harmful substances like hydrogen sulfide and ammonia, which are toxic to remaining life and can compromise water quality for human use.
