In spite of being a pest this plant is promoted according to the site of National Freshwater Prawn Research and Training Centre, Inland Fisheries Division, Department of Fisheries, Ministry of Agriculture and Cooperatives in Thailand to be useful in prawn-farms: “Provision of water lilies such as ‘Paktobjava’ (a Thai aquatic plant) in the rearing ponds in sufficient quantity will help in providing shade and hiding places for prawns and also prevent the water becoming so easily polluted. The roots of these plants will also serve as additional food for prawns.”
THE OTHER SIDE OF THE STORY:
Environmental problems associated with the water hyacinth are exuberated in warm areas where the weed grows throughout the year and develops into dense large, free-floating, monospecific islands or mats which compete with other aquatic species for light, nutrients and oxygen (Gopal 1987, in Batcher Undated; FDEP Undated; Toft 2000). These mats shade out native submersed plant species and uproot native emergent species (FDEP Undated). They reduce dissolved oxygen levels and light, significantly altering ecosystems and plant and animal communities. Low oxygen levels harms native fish populations (FDEP Undated) and fish spawning areas may be reduced, as well as critical waterfowl habitat degraded (Schmitz et al. 1993, in Batcher Undated). Mats also deposit large amounts of organic matter which increases the organic content of sediments and greatly accelerates succession patterns, allowing emergent and riparian vegetation to colonise (Penfound and Earle 1948, Trivedy et al. 1978, Gopal 1987, Woods 1997, in Toft 2000).
Originally from South America, Eichhornia crassipes is one of the worst aquatic weeds in the world. Its beautiful, large purple and violet flowers make it a popular ornamental plant for ponds. It is now found in more than 50 countries on five continents. Water hyacinth is a very fast growing plant, with populations known to double in as little as 12 days. Infestations of this weed block waterways, limiting boat traffic, swimming and fishing. Water hyacinth also prevents sunlight and oxygen from reaching the water column and submerged plants. Its shading and crowding of native aquatic plants dramatically reduces biological diversity in aquatic ecosystems.