Hundreds of fish have died in the Olifants River about 15km from Olifants camp in the Kruger National Park (KNP) as the river dries up.
Dr Thomas Gyedu-Ababio, the KNP’s aquatic biodiversity conservation manager, said the fish are believed to have died from oxygen starvation.
Gyedu-Ababio found at least 500 dead fish on the banks of a pool in what remains of the Olifants River when he visited the site recently. The 500 fish were what remained after birds had feasted on the dead fish, Gyedu-Ababio said. They were mostly catfish, yellowfish and tilapia.
Once the Olifants River was one of the largest continuously flowing rivers in South Africa, but at this time of year it is reduced to a series of pools in the KNP, kept alive by water released from the Phalaborwa barrage.
Balule camp had no water on Monday because the Olifants’ flow is so diminished.
Hippos are forced to congregate in the remaining pools of water. In the pool where the fish died, Gyedu-Ababio found almost 100 hippos in less than 500m.
In a reversal of their normal behaviour, Gyedu-Ababio said, ”the hippos ran out of the water when they saw people”, as there was not enough water in the pool to cover them.
The hippos have been living and defecating in the pools, producing an excessive quantity of dung that is now decomposing. The decomposition removes oxygen from the water, causing the fish to suffocate. Fish jumping out of the water in other pools is also a sign of oxygen shortage.
The Phalaborwa barrage is required to release water for the ecological needs of the Olifants River, but also has to provide water for human use. Gyedu-Ababio said the flow out of the barrage for several days prior to the fish deaths was so low that the gauging weir in the park could not accurately measure it.
The barrage has very limited water storage, as almost 90% of the dam is occupied by silt. It is estimated that there is only enough water in the barrage when it is full for two to three days’ water supply. In the dry season, the barrage relies on water releases from the Blyde Dam to boost the flow of the Olifants River.
Measurements of water flow at the gauging weir in the KNP show that the flow into the park is what it would be during drought conditions. The park has requested a higher flow from the barrage, as the Olifants River is not reaching Balule camp.
The silt in the barrage is to be the subject of an environmental study that went out to tender in February. The tender has yet to be awarded, the Lepelle Northern Water authority said.
The release of large volumes of silt-laden water from the barrage has previously caused fish deaths in the Olifants.
The silt is largely derived from soil erosion caused by poor agricultural practices further upstream in the Olifants River, in Sekhukhuneland. — Sapa