As an angler and a fisheries biologist, I'm a big fan of aquatic vegetation. Our waters, particularly southern reservoirs, need more vegetation.

But water hyacinth is one plant our waters absolutely do not need. Even though I've flipped a good number of outsized bass from hyacinth mats in Florida, water hyacinths are near the top of my list of threats to Mississippi fisheries.

Water hyacinths have some desirable characteristics. The lush, bright green plants and showy, purple flowers make nice scenery. That's what people thought when, so the story goes, they exported hyacinths from a Brazilian aquatic garden at the 1884 New Orleans World's Fair to the St. Johns River in Florida.

The dense growth of roots hanging in the water below each plant provides home to dozens, even hundreds, of aquatic invertebrates that provide food for numerous fish. The thick root system also filters and clears the water.

These characteristics would make water hyacinths an asset if they grew as a narrow fringe along shore or maybe as small patches entangled in standing timber. Unfortunately the plants don't grow in narrow fringes or small patches. Quite the contrary, the plants quickly multiply and cover vast areas. The purple plague.

Mississippi's warm summers and fertile waters provide a healthy climate for water hyacinths. Although the plants produce seeds, most expansion results from "mother" plants producing "daughter" plants.

Like Bermuda grass, one plant will send out a rhizome that will sprout another plant. A single, healthy plant can produce more than 500 plants by the end of the growing season.

Woven together by a meshwork of rhizomes, dense mats of water hyacinths can completely blanket hundreds of acres of waters. Waves or boat traffic can break off pieces of the mat that then drift to another location and expand. The purple plague spreads.

The rapid growth and dense mats block light to the water. No light, no photosynthesis by phytoplankton and other rooted plants. No photosynthesis, no oxygen. And no fish.

The water hyacinth is a multi-million dollar problem in Florida, where the plant rapidly expands in the tropical and subtropical climate. In addition to biological problems that ultimately impact fish, water hyacinths block boater access, impede navigation and reduce water flows. Evapotranspiration by the abundant plants accelerates water loss. Through much of the south, our waterways need more water, not less.

The multiple biological and social problems necessitate control, and millions of dollars are spent annually to reduce water hyacinths. Although some biological control agents are used to suppress hyacinths, most control is with chemical herbicides. Treatment costs are at least $100 per acre per application, and several herbicide applications are usually required throughout a year.

In Mississippi, there are no special funds available for aquatic plant control, according to Dennis Riecke, MDWFP fisheries biologist. The costs of hyacinth control on state-owned waters must come from fisheries management funds. In other words, important fisheries management activities go unfunded if money needs to be spent to control hyacinths.

Water hyacinth grows rapidly in Mississippi's warm climate, but winters are tough on the plant. Sub-freezing temperatures in the winter are common to most of Mississippi, and the cold zaps this tropical invader. The luxurious green mats of summer and fall turn brown as the freeze-killed plants decompose.

Several months after the winter kill, the decomposing plants lose their buoyancy and sink. This triggers a sequence of biological events that probably has greater impact on fisheries than the living, growing plants. The hyacinth mats continue to decompose after they sink, stripping oxygen from the water. In the absence of oxygen, the decomposition process slows.

Because tons of dead plant matter is added all at once when the mat sinks, a large amount of the plant material remains undecomposed after a year. A few plants, sheltered from the cold by taller plants, survive to propagate more hyacinths throughout the summer and fall. The winter-kill process repeats.

After several years, the area has developed a bottom with a thick layer of undecomposed plant material. The organic matter continues to suck oxygen from the water, and the unstable, peat moss-like bottom is unusable by fish and other aquatic life. Over several years, the build-up of plant material makes the water shallower. We lose fish habitat. And we lose fishing habitat.

Water hyacinths, like other exotic aquatic life, are here to stay. Control of problem areas is expensive but essential, and researchers continue to seek more effective and economical controls.

Anglers and boaters must help prevent the spread of the purple plague. One plant on a boat trailer can produce hundreds of daughter plants. Make sure you don't transport water hyacinths, or any other aquatic plant, from one water to another.