Hundreds of fish have died in the Olifants River about 15 km from Olifants Camp in the Kruger National Park (KNP). According to Dr Thomas Gyedu-Ababio, KNP’s aquatic biodiversity conservation manager, the fish are believed to have died from oxygen starvation. Excluding the dead fish eaten by feasting birds, Gyedu-Ababio found at least 500 fish lying dead on the banks of one particular pool in what remains of the Olifants River.
The fish were mostly catfish, yellowfish and tilapia. He was alerted to the problem by field ranger Claire Ntshane and visited the site on Wednesday August 24, 2005. Once the Olifants River was one of the largest continuously flowing rivers in South Africa. At this time of year, it is now reduced to a series of pools in Kruger, kept alive by water released from the Phalaborwa Barrage.
At the time of going to press, Balule Camp had no water as the Olifants’ flow was 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 500 metres. In a total reversal of their normal behaviour, Gyedu-Ababio says, “The hippos ran out of the water when they saw people,” as there was not enough water in the pool to cover them.
The hippo 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 and die. Fish jumping out of the water in other pools indicate oxygen shortages in these pools as well. Samples have been taken to the laboratory to confirm the probable cause of the fish deaths.
The Phalaborwa Barrage is required to release water for the ecological needs of the Olifants River, but it is also required to provide water for people’s basic needs. According to Gyedu-Ababio, 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 percent 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.
From August 18 to 24, the Blyde Dam continuously released water for the barrage on request from Lepelle Northern Water, increasing the flow by a factor of six from the 22nd to the 24th. The water is estimated to take three days to reach the barrage, and so should have reached the barrage a few days prior to the fish deaths.
At this point, measurements of water flow at the gauging weir in the Kruger Park show that the flow into the park is what is would be during drought conditions. The park has had to request a higher flow from the barrage as the Olifants River is not reaching Balule Camp, and there is no water in the camp at the time of going to press.