Water hyacinth is widely recognised as the world's worst aquaric weed. Originally exported from its native Amazonia because of its attractive flowers, the species rapidly established and spread throughout tropical, subtropical and warm temperate regions of the world. Water hyacinth forms a dense impenetrable mat across the water surface, limiting access by man, animals and machinery. Navigation and fishing are obstructed, and irrigation and drainage systems become blocked. The consequences are devasting for those communities reliant on water bodies for water, food, sanitation and transport. Programs to control its growth have been initiated in most countries where it occurs. A number of biological control agents have now been introduced into these countries. As so much research has been done, these and other control agents are available and can be introduced into new regions comparatively cheaply.