The Orange River is our primary surface water source towards both human health and economic growth in the Northern Cape.  Farmers use its water to grow crops, especially grapes, which are a big part of local agricultural economy. People living nearby, and further away, also depend on the river for clean drinking water. The river is also home to biodiversity like fish, macroinvertebrates and amphibians.  Accordingly, should the Orange River’s health deteriorate the communities, farmers and biodiversity would be gravely impacted. In essence, we all need healthy water to survive. By keeping the river clean and healthy, it can continue to support both people, economies and nature for the current and future generations.

The Research Unit recently monitored the health of the Orange River at twelve sites between Prieska and Richtersveld. The aim was to see how healthy the river is and whether it can support freshwater species which are also indicators of ecological river health.

Methodology:

Macroinvertebrate Sampling

Small aquatic organisms were collected using the SASS5 net method. These organisms, known as macroinvertebrates, are important indicators of river health. Different species have different levels of tolerance to pollution. In polluted rivers, you mostly find species that can survive in poor water conditions. In contrast, clean rivers support species that are sensitive to water quality and can only live in healthy environments.

To get a fuller picture of the river’s condition, the key water quality parameters were also measured directly in the river. These included pH (acidity or alkalinity), temperature, salinity (salt levels), electrical conductivity (EC), total dissolved solids (TDS), and oxidation-reduction potential (ORP). Each of these factors plays a role in the survival of aquatic life:

• pH affects the chemical balance of the water and the ability of organisms to absorb nutrients.
• Temperature influences oxygen levels and the metabolism of aquatic animals.
• Salinity impacts freshwater species, which may not survive in salty conditions.
• EC and TDS show how many dissolved substances are in the water, which can come from pollution or natural sources.
• ORP helps indicate how well the water can support life by showing its ability to break down waste and support oxygen-rich conditions.

These measurements help to understand not just what lives in the river, but why those organisms are there. This combined approach gives a broader, more accurate picture of the river’s health and helps guide decisions towards managing and protecting it.

Key Findings

Water quality was mostly good across the surveyed sites, meaning the river can support sensitive aquatic species that need clean conditions to survive. Many macroinvertebrates living in different habitats such as stones (both in flowing and still water), gravel, sand, mud, and plants were found along the riverbanks. Common families included Atydae (freshwater shrimp), Baetidae (with three species of mayflies), Leptoceridae, Perlidae (stoneflies), Heptagenidae (Flat-headed mayflies), and Leptophilidae (Prong-gilled mayflies). Their presence is a strong sign that the river ecosystem is healthy.

At the Vioolsdrift site a lot of filamentous green algae were noticed covering the stones. This usually means there are too many nutrients in the water especially nitrates which often come from farm fertilizers and sewage. Too much algae can reduce oxygen levels and harm aquatic life if not managed, disrupting ecosystem health in the river. This suggests a cautionary note that pollution impacts upstream should be monitored and rectified to prevent deterioration of downstream river health. At the Ai-Ais Richtersveld sites, scientists found high numbers of Simulidae (blackfly larvae), along with moderate numbers of Hydrophysicids and leeches. Although blackflies can be a nuisance, their presence actually shows that the water has good oxygen levels, which is important for supporting aquatic life.

In conclusion, the current health of the Orange River is in good condition. It supports a wide range of aquatic life and provides clean water for farming, drinking, and the environment. Continued care and monitoring will help keep it that way.

By Peter Ramollo, Aquatic Scientist