The seven species of water hyacinths comprise the genus Eichhornia of free-floating perennial aquatic plants native to tropical South America. With broad, thick and glossy ovate leaves, water hyacinths may rise some 1 metre in height. The leaves are 10-20 cm across, supported above the water surface by long, spongy and bulbous stalks. The feathery, freely hanging roots are purplish black. An erect stalk supports a single spike of 8-15 conspicuously attractive flowers, mostly lavender to pinkish in colour with six petals. When not in bloom, water hyacinth may be mistaken for frog's-bit (Limnobium spongia).

One of the fastest growing plants known, water hyacinth reproduces primarily by way of runners or stolons, eventually forming daughter plants. They may also reproduce via seeds. The common water hyacinth (Eichhornia crassipes) is a vigorous grower known to double its population in two weeks.