Biologists wrestle alligatorweed on Arkansas lakes

Biologists wrestle alligatorweed on Arkansas lakes

LITTLE ROCK (AGFC) – Fish and anglers love aquatic vegetation. What's not to like? It provides food, shelter, oxygen and shade. But too much of a good thing is always a recipe for disaster. Each year, Arkansas Game and Fish biologists spend thousands of dollars trying to control nuisance aquatic plants.

One species in particular, alligatorweed has commanded the better part of biologists attention and resources in central Arkansas lakes like Conway for the last 15 years. Alligatorweed hitched a ride to the United States from South America in the ballasts of ships in the late 1890s. It first appeared in Florida and Alabama, but has since spread as far west as California and as far north as Illinois.

Alligatorweed is a perennial plant that occurs both on land and in shallow water. It thrives in subtropical and temperate climates, and prefers temperatures above 60 degrees, which means it flourishes in Arkansas for six to seven months each year. Plants growing in floating mats have hollow stems which makes the plants buoyant. The stems intertwine making the mats very dense and impossible to navigate through with boats. Floating mats are easily distributed thought a waterbody by wind or current, until it gets snagged on a tree or pushed up onto the bank where it will quickly spread and takeover and choke out shoreline or open water habitats.

The plant can spread by seeds, but most often grows from buds and fragments of existing plants, which makes eliminating the nuisance plant extremely difficult.

"Essentially, every little piece of plant that is broken off of the main stem has the potential to create a new plant and mat of vegetation," said Matthew Horton, AGFC habitat biologist in Mayflower. "Add in that it can grow almost 4 inches a day and extend over 3 feet above the ground or water, and you can see how easily it could overrun a lake."

Horton says many aquatic plants can be controlled with a combination of mechanical removal, chemical sprays and placing insects or fish in the area that will eat the vegetation, but that's not the case with alligatorweed.

"Grass carp and alligatorweed flea beetles have proven unreliable and inefficient at controlling the plant in Arkansas," Horton said. "Mechanical removal causes fragmentation of the plants which only exacerbates infestation. Some herbicides, rated for aquatic use, have proven effective at killing the plants but it is impossible to kill every little plant on a waterbody."

Horton says chemical treatments on Conway have to be done by airboat because of the shallow water and dense mats that already block access to much of the vegetation.

"It's very expensive, and those dollars and manpower could be going to habitat work to improve the fishery instead of fighting a constant battle with this plant," Horton said.

Some anglers still like alligatorweed, particularly because crappie and bass tend to hide under its dormant mats in fall, winter and early spring. However, the plant's negatives far outweigh its positives. It chokes out native plant species crappie, sunfish and bass need for nursery and spawning habitat. It can change the water chemistry and cause low oxygen levels in shallow water, which pushes fish out and can even cause fish kills. The most visible problem with alligatorweed is that it blocks boating and fishing access, and can completely overtake small ponds, lakes and wetlands.

Biologists have been fighting alligatorweed on Lake Conway for more than a decade, but the nuisance plant was discovered in Lake Overcup in 2014 as well.

"Even after meticulous chemical treatment, it has established itself along 90 percent of the lake's shoreline," Horton said. "It is not a major nuisance in Overcup yet, but if left unchecked, even for one year, it could choke out a significant portion of the lake's shoreline and shallow coves. "

Horton says Lake Cargile is the latest waterbody in central Arkansas to see the invasive plant.

"We saw it in Cargile for the first time this spring, and we'll try our best to eliminate it," Horton said. "But once it's established, complete removal can be nearly impossible." Horton says the spread to Overcup and Cargile is likely the result of small pieces clinging to boats and trailers transported from Lake Conway and the Arkansas River, where the plant is abundant. He says "Clean, Drain and Dry" is more than a catchy tagline, it's quickly becoming the mantra for many agencies battling invasive species.

"Anglers are our front line in helping stop the spread of invasive aquatic species," Horton said. "Completely removing any pieces of vegetation from boats, waders, nets and other fishing equipment is extremely important when battling these types of vegetation. Make sure all the water is drained from live wells and bilge areas in the boat, and if possible let everything dry out before taking your boat or equipment to a new body of water."

If you see an unfamiliar plant species taking over a part of your favorite fishing lake, contact your local fisheries biologist to see if they are aware of the plants. They can issue permits to people who own property adjacent to Commission-owned lakes to help spray approved aquatic herbicides next to their property. Visit to find your local regional office and fisheries biologist.