Fish Die-Off Phenomenon in the Waters of Lake Nubia near Halfa
Investigation and Editing: Engineer Abdelrahman Mohammed Zain (Magdi)
The Citizen Newspaper
Three Experts Open the File: Dr. Samah Makawi Warns of Algal Toxins, Dr. Sahr Badri Al-Nour Explains Wind and Depth Factors, and Dr. Adel Abdullah Describes Why Halfa is “Sudan’s Drain” and Why Kosti May Be the Next Disaster
In recent days, Lake Nubia in the Wadi Halfa region witnessed a sudden environmental phenomenon characterized by the mass death of fish, a change in water color to yellowish-green, and the emission of foul odors. The incident sparked scientific debate between those attributing it to global warming and others referring to “eutrophication.” To provide a comprehensive view, The Citizen Newspaper interviewed three experts from different disciplines, each presenting their interpretation to complete the scientific picture.
First: Dr. Samah Makawi
(Lecturer – Department of Zoology, University of Khartoum – Freshwater Biology Specialist)
“Green color and strong odor indicate a dangerous algal bloom… boiling does not help”
Dr. Samah Makawi stated during her participation in the first seminar on the impacts of artisanal mining, organized by the Sudanese Society for Environmental Protection on Friday, April 24, 2026:
“What we observe in Lake Nubia—fish die-offs, greenish water color, and strong odor—are indicators of what is scientifically known as a Harmful Algal Bloom (HAB), particularly cyanobacteria (blue-green algae). This phenomenon is known in the Nile, but its current scale is alarming.”
She added:
“Fish deaths are most likely caused by oxygen depletion due to excessive algal growth. Algae consume oxygen at night, leading to fish suffocation in the early morning. Some of these algae also produce toxins (microcystins) that affect the liver and nervous system.”
Drinking water warning:
“Water may not be safe if it appears green, has odor, or altered taste. Boiling does not remove algal toxins; it may rupture cells and release more toxins. Activated carbon filters may help if available, and water should be drawn from deeper unaffected zones. Children and animals must not drink from it. In severe blooms, bottled or alternative safe water sources are the only reliable option.”
Second: Dr. Sahr Badri Al-Nour
(Professor of Fisheries – Faculty of Agricultural Production Technology – Africa International University)
“Global warming is not the only suspect… wind and depth are critical factors”
Dr. Sahr Badri Al-Nour provided a more analytical interpretation:
“Dr. Samah’s explanation regarding oxygen depletion due to nutrient-driven algal growth is valid as a primary hypothesis. However, it is not the only contributing factor.”
Timing of the event
“Fish died in the early morning, when temperatures are lowest. This weakens the argument that heat alone is responsible. The main issue is dissolved oxygen depletion, which reaches its minimum after nighttime consumption by algae. Global warming acts as an amplifying factor rather than the direct cause.”
Wind and oxygen exchange
“Wind plays a crucial role in oxygenation through wave activity. In the days before the incident, wind activity appears to have been weak, reducing oxygen mixing and creating stagnant conditions.”
Lake system behavior
“Lake Nubia is a slow-moving, shallow system. Such environments are naturally more vulnerable to oxygen depletion, especially at night. Species with air-breathing capability survive longer than gill-dependent fish.”
Need for scientific confirmation
“Accurate diagnosis requires laboratory data: dissolved oxygen (DO), biochemical oxygen demand (BOD), temperature profiles, algal species identification, and fish tissue analysis.”
Third: Dr. Adel Abdullah
(Expert in Contour Geography and Hydrology)
“Wadi Halfa is Sudan’s drain… and Kosti is the next risk zone”
Dr. Adel Abdullah provided a hydrological explanation of the phenomenon:
“This is not an isolated event; it is part of a larger hydrological system behavior.”
Why Halfa is vulnerable
“Wadi Halfa is the lowest elevation point in Sudan’s Nile system. The natural slope causes pollutants from upstream agricultural and urban areas to accumulate in this region. Combined with slow water movement behind the High Dam, this creates a trap for nutrient accumulation and algal growth.”
Why the White Nile near Kosti is a future risk
“The White Nile between Kosti and Khartoum has extremely low gradient—only about 6 meters over 400 km. This results in very slow flow, wide shallow water, and high heating rates. These are ideal conditions for large-scale algal blooms if nutrient loading increases.”
Groundwater concern
“The Nubian Sandstone Aquifer, one of the world’s largest freshwater reservoirs, may face long-term contamination if surface toxins infiltrate through geological layers.”
“Surface pollution today represents a delayed risk to future drinking water security.”
Summary and Recommendations
Engineer Abdelrahman Mohammed Zain (Magdi)
Key conclusions:
Fish death is primarily caused by oxygen depletion due to eutrophication and algal bloom.
Climate change contributes indirectly but is not the sole cause.
Wadi Halfa functions as a natural pollutant accumulation zone.
The White Nile (Kosti–Al-Duwaym region) is a high-risk future zone.
Groundwater systems may face delayed contamination risks.
Boiling water does not neutralize algal toxins.
Urgent recommendations:
Establish early warning monitoring systems for Lake Nubia and the White Nile.
Treat agricultural and sewage discharge before entering the Nile.
Educate communities about the risks of green water and boiling limitations.
Conduct hydrogeological studies on contaminant migration to groundwater.
Provide safe alternative drinking water sources in affected areas.
Final warning:
If water appears green, smells bad, or fish deaths are observed—do not drink it even after boiling. Contact environmental authorities immediately.
Science is not for fear—it is for timely action and prevention.
Scientific References
WHO – Cyanobacterial toxins in drinking water:
https://www.who.int/news-room/fact-sheets/detail/cyanobacterial-toxins-in-drinking-water
US EPA – Harmful Algal Blooms:
https://www.epa.gov/nutrientpollution/harmful-algal-blooms
FAO – Eutrophication and aquatic ecosystems:
https://www.fao.org/fishery/en/topic/13539
USGS – Algal blooms and oxygen depletion:
https://www.usgs.gov/special-topics/water-science-school/science/algal-blooms