Pretty poison: Invasive plant chokes an Arkansas lake

By Mary Elizabeth Williams-Villano

It has lush purple blooms, but its effect on fish and other aquatic life is anything but beautiful.

Common water hyacinth
John D. Byrd Mississippi State University

Looking at this pretty aquatic plant with its floating carpet of green leaves and lovely lilac flowers, it’s hard to believe that it’s deadly for everything that lies beneath it. It’s called water hyacinth, and it’s a big problem for the Arkansas Game and Fish Commission, according to a story in the Magnolia Banner News.

The Commission’s biologists have battled the invasive plant since 2005 when it was first discovered in a southeast Arkansas lake.

“Water hyacinth likely will never be eradicated from Lake Wallace, as the lake has an established seed base of the plant,” Kris Nault, fisheries supervisor for the AGFC in Monticello says in the story. “But by keeping up with treating it and some help from Mother Nature in the form of some cold winter days to knock it back, we can keep it at a reasonable level where anglers and boaters can still enjoy the lake.”

Part of the problem with this plant is its incredibly fast growth rate. “The growth rate of water hyacinth is among the highest of any known plant,” Nault is quoted as saying. “In ideal conditions, water hyacinth populations can double in size every two weeks. At that rate, it doesn’t take long to become an issue with angling access, boating access and the lake itself.”

Just one healthy acre of water hyacinth can weigh more than 200 tons, according to the University of Florida’s Center for Aquatic and Invasive Plants. The plant forms thick mats that create impassable barriers to boaters and anglers. Worse still, these mats effectively form a blanket that smothers all aquatic life underneath, sucking oxygen out of the water and shading sunlight,

“Decomposing water hyacinth mats can also lead to muck accumulation on the bottom,” Nault says in the story. “That can make lakes shallower over time and change the entire system.”

Water hyacinth isn’t new to the U.S. It first arrived in the United States at the 1884 World’s Industrial and Cotton Centennial Exposition in New Orleans. Visiting groups from Japan brought the native South American plants to the Exposition and gave them away to people. By the turn of 20th century, it had spread throughout the Southeast. By 1904, people had spread the noxious weed as far as California.

Bayous and waterways were soon clogged with massive mats of the plants, becoming a nuisance for both commercial and recreational boat traffic. They also choked out once fertile fishing areas.

In 1910, Rep. Robert Broussard of Louisiana introduced H.R. 23261, asking for $250,000 to import hyacinth-eating hippopotamuses, also touted as a supply of meat. But the measure failed, along with the notion of “lake steaks” from Louisiana hippo ranches.

Today, biologists turn to herbicides to control water hyacinth plants. Biologists spray them with glyphosate, which is low in toxicity to fish and wildlife, but it still proves difficult to combat. Part of the reason is that the large mats of the plant are composed of many layers. The top layer may shield leaves and stems of other plants underneath, requiring multiple treatments to reach all the plants in the mat.

“The herbicide must be absorbed into the plant’s tissue, then it will kill the entire plant,” Nault told the reporter. “The process often takes up to two weeks.”

It’s been effective at controlling the plant in Lake Wallace, but it’s a constant battle. This spring, biologists mapped out the area the plant covered, about 18%. Several treatments later, its coverage has been reduced to about 5% of the lake’s surface.

“Boating the lake is much easier now,” Nault says in the story. “Areas that were impassable due to rafts of water hyacinth mats are now clear enough to move around.”

The story reports that Jimmy Barnett, coordinator for the AGFC’s Aquatic Nuisance Species Program, says the best method to battle problem plants like water hyacinth is to prevent them from ever reaching other bodies of water.

A major source of the spread of invasive plants is boaters and anglers unintentionally transporting bits of plants or their seeds on their boats and equipment. Barnett repeats the mantra, Clean, Drain and Dry, a popular slogan developed by Wildlife Forever.

In the story, people are told to “Clean any bits of vegetation and mud you find on your boats and trailers before leaving the lake. Drain all the water from the boat’s bilge area and live wells. Let everything dry out at least five days before visiting a new body of water. If you can’t wait that long, rinse the boat and trailer thoroughly with a high pressure washer or hot water that’s at least 120 degrees to help remove any invasive organisms.”