Rietvlei Nature Reserve belongs to the City of Tshwane Metropolitan Municipality and was established to supply the city with clean drinking water. The dam and a part of its catchment area were proclaimed as a nature reserve and is managed as such. The main aims of the reserve are -

• to supply the city with clean drinking water;
• to protect and conserve a sample of the natural environment around the city in a relatively pristine state;
• to conserve genetic diversity and stop the loss of species;
• to make live game available for relocation when available;
• to give local and foreign visitors the opportunity to visit the reserve, get into the veld and take part in the activities; and
• to supply facilities and opportunities for environmental education, research and monitoring.

Sound conservation, scientific and research principles are used in the management of the reserve.

Rietvlei Nature Reserve falls in a summer rainfall area and has an average rainfall of 724 mm a year. The summer temperatures can go as high as 34 °C and the winter temperatures as low as -2 °C. The winters are dry and frost occurs regularly. It is a typical highveld climate.

The reserve consists of open grassland with undulating hills. The height above sea level is 1 525 m (5 000 feet), the highest point being 1 542 m and the lowest point (at the dam's overflow) being 1 475,84 m. The Sesmylspruit flows into the Marais Dam, where the water overflows. Later it joins the Grootvleispruit which flows through the reserve and forms an 8 km vlei or wetland. The dam has a storing capacity of 12,024 million m³ of water and a surface area of 204,13 ha when full. The dam wall is 32 m high and 350 m long. At the wall the dam is 16 m deep. The overflow of the dam is 191 m long and 101 m wide. The catchment area of the dam covers 479 km², but the Rietvlei Nature Reserve covers only 38,70 km² (3 870 ha). In the dry winter months, more than 20 million litres of water flows into the dam a day. The wetland is actually a peatland and therefore an excellent natural filter and sponge.

The supply of clean drinking water and the protection of the catchment area are the main reasons for the establishment and maintenance of the reserve. There are three sources of water on the reserve, namely the dam with its purification plant below the dam wall, five fountains and five boreholes. The reserve supplies about 15% of the city's drinking water, which equals about 40 million litres of water a day.

Rietvlei Nature Reserve is situated in the central variation of Bankenveld 61b, which forms part of the false grassland types (Acockc, 1988). It is also described in Low and Rebelo's book Vegetation of South Africa, Lesotho and Swaziland (1996) as "rocky highveld grassland" (34), which is part of the grassland biome.

It is a moist, temperate grassland and transitional area between true highveld grassland and bushveld. This is why you find grassland and bushveld birds on the reserve. The reserve also has a fire climax veld type and for the largest part consists of sour veld, although the vlei areas are more palatable. Although grasses are the most visible plants on the reserve (73 species have been recorded), herbs and forbs (herbaceous plants) are plentiful.

The entire reserve except the vlei or wetland system is burned in a three-year cycle. In other words, a third of the reserve is burnt a year. The reserve is divided into about 48 burning blocks, with the roads acting as firebreaks. The burning takes place at the end of the winter after the first 10 to 15 mm of rain and the first thunderstorms. Burning is done at night when it is cool and the soil is moist. This prevents damage to the soils and the underground parts of plants. The burning is also done against the wind, which creates a low-intensity, slow-burning veld fire. No reed beds are burnt.

If no burning takes place, more and more trees will take root and the grass layer will become so thick that all new growth of the current vegetation will be smothered. Dead plant material will not become available to new growth, and many of the herbs and forbs will not flower, nor will their seeds germinate.

Fires are kept out of the wetland area at all costs to prevent the peatland from burning. The reeds that grow in the vlei fall over with floods, but because of the low-energy system and lack of oxygen, the plants do not decompose and become part of the peat layer. This organic layer can only be preserved if it is permanently wet and never burns. The wetland is the reserve's most important asset.

Many rare and threatened or impressive plant species can be found on the reserve, for example:

• Erythrina zeyheri
• Ziziphus zeyheriana
• Many Crinum spp.
• 6 Hypoxis spp.
• Boophane disticha
• Many Ipomoea spp.
• Lithops sp.
• Scadoxus puniceus
• Protea welwitschii.

As far as geology is concerned, the eastern part of the reserve is mainly made up of dolomite and chert. The central parts, from north to south, consist of andesitic lava with agglomerate, shale and tuff layered in between. The western ridges contain mainly shale and siltstone, and here and there quartzite and grit stone on top with layers of tillite and limestone. Between the lava and dolomite there are also strips of shale and quartzite ridges. Many sinkholes (doline) can be found in the eastern dolomitic parts of the reserve.

The most prominent feature of the soils on the reserve is their shallowness. Where a B-horizon can be found, it is very thin and layered. The limiting layers are mainly lava, quartzite, diabase or dolerite. The soils are also very prone to erosion. In and adjacent to the wetlands the soils have a high clay and organic material content and are regularly flooded.

The blesbuck and black wildebeest are endemic to the Southern African highveld. The reserve is also situated on several transitional areas from east to west and north to south. This is why the veld type can also be called a "change-over veld type" between true grassland and true bushveld. The blesbuck and black wildebeest never occurred naturally north of the Magaliesberg range. The springbuck never occurred naturally further east than Rietvlei Nature Reserve for very long periods. Other species such as the suricate and bat-eared fox are also found on the reserve, even though they are more common towards the drier west. More than 20 large mammals can be seen and 270 species of birds have been identified and confirmed on the reserve.

Dangerous animals include ostrich, buffalo, rhinoceros, snakes en hippopotamus.

Many species of snakes and other reptiles have been recorded on Rietvlei. The most common species are the leopard tortoise, puff adder, rinkhals, brown house snake and spotted skaapsteker. Rietvlei is also home to all 12 the amphibian species that occur in this quarter degree square. The reserve is particularly important for protecting the breeding and foraging habitat of the threatened giant bullfrog.

There are many servitudes on and/or across the reserve:

• Cabora Bassa power line.
• Many other power lines.
• Rand Water pipeline.
• Sewer lines.
• Petronet petrol and diesel pipeline.

The biggest threats to the reserve are development and alien or exotic species. These alien species include black, silver and green wattle, blue gum, privet, poplar, willows and many forbs.

Rietvlei Nature Reserve is important for many reasons namely:

• It is a proclaimed nature reserve in an urban area.
• Three of the Big Five or four of the Big Six can be seen on the reserve, namely: rhino, buffalo, leopard and hippo.
• Only 5% of this veld type is protected in conservation areas and more than 66% have already been changed, degraded or lost to development.
• Rietvlei has one of the largest peatlands in a protected area in South Africa.
• The reserve is unique as it is the only proclaimed Bankenveld nature reserve on a dolomite foundation in the world.
• It is a nature reserve on high-potential agricultural land with a high carrying capacity.
• The reserve has many threatened fauna and flora.

A number of historical buildings, stone walls and graves can be found on the reserve, the old farmstead being the best preserved.

The reserve caters for day visitors, organised tours, hiking, horse riding, night drives, bus tours, angling and environmental education.

Rules on the reserve:

• Visitors must stay in their vehicles; they are only allowed to get out at the picnic site and bird hides, at their own risk.
• The speed limit is 30 km/h. Some roads are closed to the public mainly because they lead to the fences or are inaccessible to ordinary vehicles.
• No pets are allowed.
• Fires are only permitted at the picnic sites.