Draining an area of just under 1million km2 or 77% of the land area of South Africa, the Orange River has its source in the Drakensberg mountains, but starts as the Senqu River in Lesotho. From here it flows westwards to the Atlantic Ocean. Here, it can be seen flowing more or less horizontally across the upper left quadrant of the image.
The headwaters are located at an altitude of 3300 m and consequently parts freeze in the winter months. After the town of Kimberly the river is joined by the Vaal river, its main tributary and from here it enters the arid region of the southern Kalahari and Namib desert. Dams along the river provide water for irrigation and hydropower, however because of the unpredictable flow and sand bar at the river mouth navigation is limited.
Given the length of the Orange River, combined with its range of altitude and climacteric zones, the basin covers a wide range of ecological systems, and can be regarded as being a linear oasis. Its bio-geographical isolation means that potential for re-colonisation from adjacent rivers and wetlands is very low. The river biota is therefore unusually susceptible to the permanent loss of species.
Its biomes contain a vast array of faunal and floral species variety with several endemic species. However, they also comprise areas facing environmental threats, such as the extinction of species and changes brought about by desertification. The economic utilisation of the Orange River’s water as well as the land use patterns in the basin strongly influences the environmental state of the river basin.
In this context four issues are of particular significance, namely the problem of soil erosion and wetland losses in Lesotho (the most severe problem), the impact of industrial and municipal effluent in the Vaal River system, agricultural pollution in the Vaal and Orange River and the environmental threats to the Orange River Estuary Ramsar site at the mouth (click here for more information).