DAR ES SALAAM, Tanzania

Authorities in the East African country of Tanzania have banned fishing in the transboundary Mara River after a toxic spill of cow excrement and urine caused pollution that killed hundreds of fish, harming people's livelihoods.

Piles of dead tilapia fish have been washing up on the river's banks, threatening the incomes of local people who depend on fishing.

Juma Kikoka, the commissioner of Rorya District, told Anadolu Agency that fishing activities and water use in affected areas have been suspended indefinitely pending further scientific investigations.

Meanwhile, the government has instructed the local water authority in the Mara region to find an alternative water supply for the affected villages.

Deadly sludge

The move comes after an investigative team formed by Selemani Jafo, minister of state in the vice president's office responsible for union and environment, revealed that toxic cow sludge and urine caused pollution that killed the fish.

Samuel Manyere, a scholar from the University of Dar es Salaam who led the investigation, said the river has been tainted by the discharge of livestock sludge and dirt from exotic plant species including water hyacinths, which had reduced the amount of oxygen in the river.

“A one-time heavy rain forced the sludge into the river and slowed its natural ability to replenish the water,” he said.

According to the investigation, about 1.8 million tons of livestock sludge and 1.5 billion liters of cow urine had been discharged into the river.

Pollution from livestock -- FARMS -- is known to clog waterways with excessive organic matter, depleting oxygen and killing other aquatic life.

Globally, freshwater ecosystems are rapidly losing their biodiversity because of increasing human activities including livestock keeping, say researchers.

Numerous studies have shown that livestock excrement contains significant amounts of nitrogen and phosphorus and that watersheds with livestock tend to have significantly higher concentrations of hazardous chemicals, said Gasper Mhinzi, a professor of chemistry at the University of Dar es Salaam.

According to him, a cattle waste effluent spill can potentially cause devastating pollution in streams and rivers.

Human activities to blame

The transboundary Mara River, which originates from the Mau forests of Kenya, drains into Lake Victoria at the city of Musoma in Tanzania. It supports the lives of thousands of people and is part of the great Serengeti ecosystem which is connected to Maasai Mara National Park of neighboring Kenya.

Increasing human activities such as settlements, industries, mining, and farming have been the source of environmental pollution in the river, threatening people's livelihoods, say local residents.

Flower Msuya, a senior researcher at the Institute of Marine Sciences of the University of Dar es Salaam, says the effluent is a significant polluting substance, starving fish and resulting in potentially massive fish kills if it enters a watercourse.

“When a river loses its dilution capacity in the dry season, the effect of a small leak can cause huge damage,” Msuya said.

Although the government has ruled out a chemical spill from a nearby gold mining site as the source of the fish deaths, environmental activists say it may be one of the reasons.

“Livestock excrement is usually soluble in water, and in fact, it is a source of food for fish and other aquatic life. How on earth can it harm or even kill fish?” said Aidan Massawe, an environmental activist.

Peter Ryoba, a local resident in Rorya District, feared poison may have killed the fish and said he was scared for his children who use the water regularly.

“I find it very strange. Cows are always roaming, and we never heard they can cause fish to die,” he said.

Death knell

A report by international wildlife non-governmental organization the World Wildlife Fund (WWF) issued in November 2020 detailed how farming, deforestation, mining, illegal fishing, and invasive species could sound the death knell for the transboundary river.

According to the report, fish are being driven to extinction in the Mara River Basin, putting the livelihoods of more than a million people in Kenya and Tanzania in jeopardy.

“When something goes wrong with the environment, it is the small species in the water that get affected first. Therefore, driving such water biodiversity to the brink will have a cascading negative effect on the rest of the ecosystem,” said William Ojwang, Africa Rift Lakes Program manager at WWF Kenya.

The Mara Basin, which covers 13,750 square kilometers (5,309 square miles), is known globally for the annual wildebeest and zebra migration, which brings in millions of dollars in tourism.

The Mara River is key to this spectacle, as it is the only source of water during the dry season.

While the river's flow has been erratic in recent years, the report says human activities such as a high level of water body_abstraction for agriculture, hydroelectricity, and tourism have been catalysts for rapid degradation.

Several small-scale goldmines in the region are responsible for discharging directly into the stream high levels of heavy metal deposits that can endanger human and fish life, the report said.

Jonas Chacha, a fishmonger in Kirumi village in the Mara region, said the government's decision to suspend fishing has severely affected his income and the welfare of his family.

“I am not able to support my family. I was earning about 30,000 Tanzanian shillings ($13) every day. That income is now gone.”