Hartbeespoort becomes 'water desert'

Hartbeespoort Dam (Image: southafrica.net)

Up to 720 megalitres of treated sewage water, mixed with litter and plant debris - from the Jukskei, Small Jukskei (both from Johannesburg), Swartspruit (from the East Rand) and Hennops (Midrand and Pretoria) rivers, as well as Modderfontein Spruit, Sandspruit and Braamfontein Spruit - flows into the Crocodile River. This all ends up in Hartbeespoort Dam saturating it with an overwhelming level of phosphates.

"We found a wrecked car had washed into the the dam," said Petrus Venter, deputy regional director for the Department of Water Affairs, who runs the management of the dam. "In 2010, we pulled a cow out of it and dead cats and dogs are a common occurrence during a flood."

The inflow of pollution has distorted the dam's ecology, which is currently dominated by only two plant species - water hyacinth and algae - and three fish species, the common carp, barbel and canary kurper.

"The definition of a biological desert is a lack of biodiversity, which is what we have in the dam," said Venter.

Biological control system

He and his team are installing an integrated biological control system for the dam, which includes floating wetlands and the removal (and replacement) of the dominant fish species and more of the the hyacinth and algae to help the water cope with pollution.

Since the project was started in 2008, several bird species, such as the cormorant and red-knobbed coot, have returned in huge numbers.

Hartbeespoort Dam was built as an irrigation dam for the province's farms but has become a popular getaway. There are several luxury housing estates surrounding the dam.

"These properties are a government cash cow, worth R30m a year in property taxes," said Venter.

In recent years people have complained bitterly about the stench emanating from the algae, which can become highly toxic.

Venter said though Johannesburg's sewage water was extremely well treated, the volumes of purified sewage running into the Crocodile River were overwhelming for the dam.

"During floods we get five times as much nutrient as the dam can cope with," he said. Some 98% of the pollution comes in from the Crocodile River.

"Though Johannesburg's northern sewerage works is operating well, some of the nine other sewerage works in the dam's catchment area are not working properly and suffer from maintenance problems," Venter said.

"This has often been the case with smaller municipalities, but now even the large sewerage works are unable to cope and that is really worrying," he added.

Source: The Times via I-Net Bridge