Popular dam a 'desert'

Pollution from 2.7million people is flowing into the Hartbeespoort Dam in North West and turning it into a "water desert".

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 and is dumped in the dam, overwhelming it with phosphates.

"There was once a car wreck that washed into the Hartbeespoort 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 and 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 - 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.

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, the hyacinth and algae to help the water cope better 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, helping with rehabilitation by eating the leaves of the hyacinth.

Hartbeespoort Dam was built as an irrigation dam for the province's farms but has become a popular holiday destination, with several luxury housing estates on its banks.

These properties are a government cash cow, worth R30-million a year in property taxes, said Venter.

In recent years people have complained bitterly about the stench of the algae, which becomes 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.

And though Johannesburg's northern sewerage works were operating well, some of the nine other sewerage works in the dam's catchment area were running into disrepair and maintenance problems, Venter said.

"It has always been the case with small municipalities, but that it is becoming the case with our gigantic [city] sewerage works is really worrying."