The Ugandan government has ruled out poisoning as the cause of large scale fish deaths on Lake Victoria as activists call for a concerted effort to stem the increased pollution of the water body, Chimp Corps report.
“Preliminary investigations have ruled out the possibility of poison as the cause of the deaths of the fish,” said National Environmental Management Authority (NEMA) in a statement this Sunday.
“The occurrence has been attributed to a drop in oxygen levels. Nile perch is species of fish known to be sensitive to low oxygen levels- (below 2mgl),” the statement added.
Communities living in and around the shores of Lake Victoria have recently been concerned by the growing number of dead fish, especially Nile Perch, being washed ashore.
They have since express fears that the Lake could be contaminated by poisonous chemicals.
The dead fish are not only an eyesore but also emit an offensive odor as the decomposition occurs.
NEMA said as a result of the recent flooding and rising water levels, large masses of weeds were submerged and sunk into the lake bed.
“These weeds use up oxygen as they rot from within the lake hence a drop in the oxygen levels.”
Seeming pristine from a distance, experts have warned, Lake Victoria is at risk of dying off from pollution.
At 26,560 square miles (69,000 square kilometers), Lake Victoria is the world’s largest freshwater lake, second only to Lake Superior in North America.
The lake is shared by East African states of Kenya (6%), Uganda (45%) and Tanzania (49%).
Lake Victoria basin is used by communities and industries as a source of food, energy, water and transport.
The lake is also a sink for human, agricultural and industrial waste.
The Lake provides employment for up to 30 million people.
The Lake’s catchment area of 258,700 square kilometers has a GDP of US$ 300-400 million and supports nearly one–third of the total population of East Africa.
The Lake is the source of River Nile, which is renown for whitewater rafting and flows to Egypt through Sudan.
While NEMA gives other reasons for the low oxygen in the lake, experts say uncontrolled pollution is mainly to blame for the crisis.
The Lake has for along time been a sink to excessive nutrients and untreated effluent that have led to fish die-offs, algal blooms and the spread of hyacinth, a ferocious waterweed.
Although mostly eradicated now, the remnants of hyacinth on Lake Victoria deplete dissolved oxygen, sunlight and are an obstacle to water transport. Along the shoreline, hyacinth provides habitat for malaria mosquitoes and snails which habour bilharzia parasites.
Nakivubo Channel Industry Discharge
In Uganda, point sources and non-point sources such as deficient sewage and industrial wastewater plants, small-scale workshops, waste oil from parking lots and car repair garages are major sources of pollution load for the lake.
The sewer system in Kampala city serves only a small fraction of the city population and only 10% of all sewage generated in Kampala gets treated.
Guesthouses, slum dwellings and industries discharging untreated wastewater in Nakivubo channel, which flows into Murchison Bay contribute lachrymal pollution load and depleted oxygen levels in Lake Victoria.
An engineer from AWE recently recorded dissolved oxygen (DO) levels of less than 2 mg/liter in Murchison Bay yet most fish species die off at DO of 4 mg/liter.
Nakivubo Channel carries approximately 75% of the nitrogen and 85% of phosphorus nutrient load discharged daily into Murchison Bay. The high nitrogen and phosphorous levels are responsible for excessive eutrophication and algal blooms seen in the Bay.
Often, Murchison Bay is covered in a green floating blanket of algae that is as viscous as wall paint.
Algal blooms clog water treatment plants, deoxygenate lake water causing fish die-offs and cause a skin condition known as swimmers itch.
NEMA, which many see as a ‘toothless dog’ in fighting pollution, blamed the recent strong winds around the lake Victoria basin, saying “they have heightened lake overturn; a phenomenon that causes water from the bottom of the lake that is low in oxygen, to come up and mix with upper layers, where fish live; leading to a reduction in oxygen, hence the death of fish.”
This is not the first time large scale fish deaths are occurring on Lake Victoria; Fishing communities have always referred to this situation as “Kaliro” and it occurs periodically.
NEMA advises communities living around the lake “to bury the dead fish to contain the pungent smell; as further research and studies are undertaken by all stakeholders including, NEMA, MAAIF, Communities, developers etc.”