What: A floating plant that grows in all types of freshwater. It ranges from a few inches to three feet, and grows lavender flowers and thick, rounded leaves with a spongy stalk that can inflate to make it float. It has dark feather-like roots.

Originated from: South America and lives in warm climates.

How it arrived: Introduced into the US in 1884 for the Cotton States Exposition in New Orleans as an ornamental for fish ponds. It escaped into the wild.

It's spreading: To the wetlands of Louisiana, a perfect home for this exotic. Map of invasion in the US.

Damage: The plant can crowd out other plants, clog machinery, and prevent navigation. Its overgrowth will lead to greater plant decay that will consume the oxygen in the water, killing fish and invertebrates.

Why it's a threat: Water hyacinth can colonize large areas in short periods of time. It's growth rate is among the highest known -- its population can double in 12 days. During a drought, it survives as seeds that remain dormant until reflooding occurs.

Control: The plant dies off naturally in harsh weather. Besides prayer, research has shown that several types of biocontrol are effective. This means using other living organisms to kill the plant. In this case, the hyacinth weevil is used to eat the plants. Biological Control Insects or Biological Control. Herbicides may also be used.