Sewage swept into the Vaal River by recent rains have all but destroyed the river’s ecosystem, Beeld newspaper reported on Tuesday.
The Eco-Care Trust, an environmental organisation committed to the conservation of fish and rivers, told the paper tonnes of dead fish have been floating downriver since the weekend.
The trust’s Bernard Venter said the fish include large numbers of largemouth and smallmouth yellowfish (Labiobarbus kimberleyensis and Labiobarbus aeneus respectively). Both are already endangered species. Other fish affected include carp and bream.
Venter said yellowfish take about seven years to reach sexual maturity.
Several generations of the fish have now been wiped out, Venter said.
He added that the fish, which can grow to 25kg, is popular with anglers because it fights furiously when hooked.
He said angling is a R1,3-billion industry and much of it takes place along the banks of the Vaal.
Marius Keet, a Department of Water Affairs and Forestry assistant director for water-quality management, said the river’s oxygen level of the river below the Klip River is very low, while the ammonia level is very high.
He believes the sewage washed into the Vaal when the Klip River flooded last week.
The result of tests for the Escherichia coli (E coli) bacteria in the water is still awaited.
E coli bacteria are a good indicator of the amount of human excrement in water.
Human waste in water is associated with numerous diseases, including dysentery, cholera and typhoid.
The dead fish suffocated because of conditions caused by the recent heavy rains, Rand Water said on Tuesday.
”The high rainfall that we experienced caused the ingress of large volumes of water into the sewage systems, and consequently overloaded the sewage treatment works,” explained catchment head Francois van Wyk.
”The silt that is scoured from the riverbeds is highly anaerobic [lacking in oxygen] due to organic matter deposited on the beds over many years.
”The combined high organic content [sewage and silt] of the water utilises the oxygen in the water to break down this organic material, and the fish consequently suffocate due to a lack of oxygen,” he said.
Conditions leading to fish deaths occurred in both the Klip and Suikerbosrand rivers, and the cumulative effect was observed in the Vaal River barrage reservoir, Van Wyk said.
There will be no impact on the quality of drinking water, and no impact on the Vaal Dam.
Rand Water said that while some of the fish are being removed from the river to a waste dump, most are being washed downstream of the Barrage.
North Rand police spokesperson Superintendent Eugene Opperman said people should stay away from the Barrage for the next 10 days.
The Gauteng police’s water wing has also been deployed to the area to warn the public not to enter the water. — Sapa