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Major problems are experienced in South Africa due to the invasion of non-indigenous or alien species of terrestrial plants in several catchments. Alien invaders are estimated to use approximately 6,7% of the estimated mean annual runoff of water over the entire area of South Africa and as high as 15,8% in the Western Cape Province. The impacts are significantly higher, on a percentage basis, during drought periods as the riparian invaders still have free access to water. Rural and urban communities with limited storage capacities for water supply that depend on the flow of water in the river are particularly affected by the reduced flow of water. The invasion of alien plants in catchments is influencing the total water resources system and affecting all sectors. The nature and extent of invasive alien plants, the effects thereof on available water resources, the threat to ecological environment and impacts on society, need to be understood to ensure the success of the integrated approach to control the spread of invasive alien plants. If properly managed, the programmes to control invasive alien plants can provide the stimulus needed for an active participatory approach in integrated management of catchments in South Africa to deal with water scarcity and to ensure sustainability of the environment, land use and water.