The most important floating aquatic weeds (FAWs) are Eichhornia crassipes, Salvinia molesta and Pistia stratiotes. E. crassipes and P. stratiotes reproduce sexually. All three species reproduce asexually. E. crassipes and S. molesta have particularly high growth rates. All can form dense mats and growth rates are increased by high nutrient levels and temperatures. Spread between continents and watersheds is largely the result of human activities. Spread within watersheds is mostly via floating propagules. FAWs are known to affect water resource management, the continued existence of human riverine and wetland communities, and conservation of biodiversity. Waterways can be blocked, and the efficiency of irrigation and hydro generation impaired. People are affected by reduction of the fish catch, inability to travel by boat and consequent isolation from gardens, markets and health services, and also changes in populations of vectors of human and animal diseases. Biodiversity can be reduced and conservation value affected. It is proposed that rational application of physical, chemical and biological control of FAWs, and reduction of nutrient input should be part of every strategy for the sustainable management of wetlands.