“The impact of the pollution is especially pronounced in Egypt, the most populous and arid nation downstream of the Nile, which depends entirely on the river as its only source of water for drinking and crop irrigation. The country currently faces one of the highest water budget deficits in Africa after decades of compensating for dwindling water supplies with intensive, large-scale wastewater reuse, the consequences of which have been understudied until now,” the scientists elucidate.

The delta’s biodiversity is also at risk, they say, and among the species facing severe threats are migrating birds which use the area as a stopover on their journey along the East African flyway.

The researchers reached this conclusion after analyzing pollution levels with eight heavy metals in samples of sediment collected from the bottom at two branches of the Nile River Delta. They found that the samples were highly polluted by esecially toxic heavy metals such as cadmium, nickel, chromium, copper, lead and zinc.

These contaminants, they say, primarily derive from untreated agricultural drainage, municipal waste and industrial wastewater. “Without proper treatment of recycled water, concentrations of heavy metals increase and are permanently embedded in the riverbed unlike organic pollutants which naturally degrade over time,” they explain in a statement on their findings.

“Heavy metal concentrations could be exacerbated by increased damming of the Nile. Mega-dams built upstream disrupt the river’s natural flow and sediment flux and thus adversely affect its ability to flush contaminants out into the Mediterranean Sea, leaving toxins to build up in bottom sediment over time,” they continue.

Alarmingly, much of this contamination by heavy merals is irreversible. However, science-based conservation measures could alleviate environmental degradation and restore the Nile River Delta’s ecosystem to relatively healthy levels.

“The aggravating water stress and the rapid population growth in Egypt, reaching above 100 million, have put local authorities in a dilemma whether to provide sufficient fresh water for the thirsty agricultural sector to secure the food supply through reusing untreated agricultural drainage water or to preserve the health of the Nile River,” says Abotalib Z. Abotalib, a postdoctoral researcher at USC Viterbi who was a co-author of the study. “The balance is challenging, and the consequences of both choices are measurable.”

“Our study underscores the need for more research on the environmental impacts of untreated water recycling and the change in river turbidity under increased upstream damming of the Nile,” the scientist adds. “Continued research with more sampling campaigns in this area could inform future conversations and collaborations among nations of the Nile River Basin, who have a shared interest toward maintaining a healthy Nile River system.”