Water hyacinth (Eichhoria crassipes).
Water hyacinth is native to South America but has naturalized and became a weed much of the Southern US. Water hyacinth is a free-floating perennial plant that can grow to a height of 3 feet. The water hyacinth has striking light blue to violet flowers located on a terminal spike.
If you want more information about this flower, just search the plant's Latin (botanical) name on Google: