Hyacinth is native floating water plant of South America but has naturalized much of the Southern U.S.
Water hyacinth is a free-floating perennial plant that can grow to a height of 3 feet. The dark green leave blades are circular to elliptical in shape attached to a spongy, inflated petiole. Underneath the water is a thick, heavily branched, dark fibrous root system. The water hyacinth has striking light blue to violet flowers located on a terminal spike. Water hyacinth is a very aggressive invader and can form thick mats. If these mats cover the entire surface of the pond they can cause oxygen depletions and fish kills. Water hyacinths should be controlled so they do not cover the entire pond.
http://aquaplant.tamu.edu/database/floating_plants/water_hyacinth.htm (http://aquaplant.tamu.edu/database/floating_plants/water_hyacinth.htm)