How Decomposing Algae Robs the Lake of Oxygen and Suffocates Aquatic Life
A pungent, sulphur-like stench rising off the surface of Lake Victoria has alarmed communities along its shoreline. Still, scientists and government officials say the smell is just the most noticeable symptom of something far more dangerous.
The Ministry of Water and Environment says the odor is caused by algal decomposition. This process is not only filling the air with foul gases but also draining the lake’s oxygen and pushing it closer to a full-blown ecological collapse.
“When these algae die and decompose, they consume oxygen and release gases like ammonia and hydrogen sulfide, resulting in unpleasant odors and hypoxic conditions detrimental to aquatic life,” the Ministry stated in a press release on April 4.
At the heart of this crisis is a process called eutrophication, where excess nutrients—especially nitrogen and phosphorus—are dumped into the lake from human activity. These nutrients, often carried in sewage, industrial waste, and farm runoff, stimulate massive algal blooms in shallow areas like Murchison Bay.
“The assessments conducted over time reveal a persistent rise in nutrient concentrations in the bay,” the Ministry said. “This creates a conducive environment for algal growth.”
Once the algae bloom, they spread quickly, covering the lake’s surface and turning it green. But their lifecycle is short-lived. When the algae die, they sink to the bottom, where bacteria begin to break them down. That’s when things get deadly.
During decomposition, bacteria feed on the dead algae in a process that consumes massive amounts of dissolved oxygen—oxygen that fish and other aquatic life need to survive.
This leads to hypoxic conditions, or oxygen depletion, particularly in shallow, stagnant zones like Murchison Bay. Without enough oxygen, fish either flee or suffocate, while bottom-dwelling organisms such as crabs, snails, and aquatic insects die off silently.
At the same time, the breakdown of organic waste releases noxious gases that pose serious environmental and health risks. Hydrogen sulfide (H₂S), recognizable by its rotten egg smell, is highly toxic to both aquatic ecosystems and human life when present in high concentrations. Similarly, ammonia (NH₃), another by-product of decomposing organic matter, contributes to further chemical imbalances in the environment, exacerbating pollution and threatening biodiversity.
The Ministry explains that this cycle is self-perpetuating:
“Upon die-off, the algal mats release the same nutrients they absorbed into their tissue back into the lake, further impregnating the water with more nutrients, and repeating the vicious cycle of new algal growth.”
In essence, the more the algae bloom and die, the more oxygen is stolen from the lake—and the more dangerous the waters become for aquatic life.
Murchison Bay, a shallow stretch of Lake Victoria near Kampala, has become the epicenter of an unfolding environmental crisis. The bay receives heavy runoff from Kampala and nearby suburbs, yet its sheltered location means the water stagnates, with little movement to flush out pollutants.
It is now choked with sewage, industrial waste, and plastic, while the surrounding wetlands—once nature’s filtration system—have been severely degraded.
“This is so because the wetland that would otherwise intercept the contaminants has been highly degraded,” the Ministry observed. The result is a nutrient trap that accelerates eutrophication far more rapidly than in the lake’s open waters.
Lake Victoria is far more than a water body—it sustains a $500 million fishing industry, provides drinking water for over 38 million people, and powers regional trade, transport, and tourism. But its oxygen levels are plummeting.
Already, fish kills, biodiversity loss, and the migration of key fish species to deeper, cleaner areas are being reported. If unchecked, vast stretches of the lake could turn into ecological dead zones—lifeless areas too oxygen-starved to support aquatic life, threatening both livelihoods and food security across the region.
To prevent Lake Victoria from reaching a point of no return, the Ministry is calling for a multi-layered rescue plan. This includes wetland restoration to revive natural filtration, and strict enforcement of the 200-meter buffer zone around the lake to block direct pollution inflows—both of which are required under the Environment Management Act.
Improvements to waste management, such as upgrading sewage systems and reducing plastic dumping, are also critical. Additionally, the Ministry advocates for sustainable farming practices to curb fertilizer runoff. Success will demand collaboration across sectors—from local communities to government agencies and environmental organizations—to restore Lake Victoria’s delicate ecological balance.
“Implementing the above measures requires coordinated efforts among different stakeholders such as local communities; Ministries, Departments and Agencies; Urban Authorities; and Environmental Organizations to restore and maintain the ecological balance of Lake Victoria,” the Ministry emphasized.
Lake Victoria’s foul smell is not just an unpleasant by-product of pollution—it is a scientific signal of distress. The decomposing algae robbing the lake of oxygen are turning a once-thriving aquatic ecosystem into a suffocating death trap.
But the science is also clear: this cycle can be broken. If Uganda takes decisive, coordinated action now—restoring wetlands, curbing pollution, and enforcing environmental laws—the lake can still be saved.
“Every Ugandan is called upon to join this crusade of protecting the environment and saving our valued Lake Victoria,” the Ministry urged.