Hydrilla Impact on Lake Ouachita in Arkansas.

In Lake Ouachita, hydrilla will effectively displaces beneficial native vegetation such as wild-celery (Vallisneria americana) and coontail (Ceratophyllum demersum). (Bates and Smith 1994) Hydrilla was first identified in Lake Ouachita in 1999 during creel surveys. Lake Ouachita is a 44,000 acre lake, with an approximate hydrilla infestation size of 4,000 acres. Hydrilla has been verified growing in waters of 24 feet with expected growth to be in the 30 - 35 foot level in the near future and due to light penetration possibly to 40 feet.

Johnny Cantrell, Biologist (retired), Lake Ouachita said that Hydrilla has a rough, sandpaper texture, and this is how you can tell the difference between it and Brazilian Elodea.

The use of the Pakistani Fly which does not kill the plant, but controls the expansion of the plant and will keep it from matting on the surface, is one attempt by the Corps of Engineers at controlling the spread of this invasive species.

Mr. Cantrell said that Hydrilla can grow one inch every 24 hours, and is an invasive, non-native species. He related how the Pakistani Fly larvae will bore into the Hydrilla stem approximately 6 to 8 feet below the waters surface to keep the Hydrilla plant from interfering with recreational boat traffic on the surface.

Hydrilla once established in Lake Ouachita will results in an array of ecosystem disruptions. Changes often begin with its invasion of deep, dark waters where most plants can not grow. Hydrilla grows aggressively and competitively, spreading through shallower areas and forming thick mats in surface waters that block sunlight penetration to native plants below.

Hydrilla was first identified in Lake Ouachita in 1999

Hydrilla Verticellata Identification:
Green, freshwater herb
Submersed plant with long slender stems
2 to 8 small, spear-like leaves per whorl spread across the water
The leaf has a sawtooth edge and small spines on the underside that are rough to the touch
Grows in as little as a few inches of water or in more than 30 feet of water.

The AGFC has stocked 10,000 grass carp in seven selected areas to contain the spread of new vegetation. Grass carp feed on vegetation, preferring Hydrilla  to the Eurasian water-milfoil.

Hydrilla Verticellata, commonly referred to as Hydrilla is a very invasive submersed freshwater herb. It was originally sold as an aquarium plant. It forms very dense strands growing from the bottom of the water and sprawling across the surface. Although it is an excellent source of food for waterfowl, it can be a serious threat to freshwater habitats and a nuisance to boaters.

Hydrilla reproduces by fragmentation. It does not form any seeds. Hydrilla produces large strands of plants in just a few months through its efficient use of low light levels and available nutrients. Even small pieces stuck on boat propellers or in bait pails contribute to the easy spread of Hydrilla to other waterways.

Hydrilla has been shown to alter the physical and chemical characteristics of lakes.

Colle and Shireman (1980) found sportfish reduced in weight and size when hydrilla occupied the majority of the water column, suggesting that foraging efficiency was reduced as open water space and natural vegetation gradients were lost. Stratification of the water column (Schmitz et al. 1993; Rizzo et al. 1996), decreased oxygen levels (Pesacreta 1988), and fish kills (Rizzo et al. 1996) have been documented. Changes in water chemistry may also be implicated in zooplankton and phytoplankton declines (Schmitz and Osborne 1984; Schmitz et al. 1993).

Hydrilla seriously affects water flow and water use.

Hydrilla, a submersed freshwater herb, does more on Lake Ouachita than fouling boat props. It also blocked marinas and choked up swimming area, raising concerns that its growing impact on recreation could upset the economy of the area.

The plant has grown explosively in Lake Ouachita in the past three to five years and is becoming as problematic as crabgrass - but it is considerably more difficult, and more expensive, to control.

Experts have told the U.S. Army Corps of Engineers, which manages Lake Ouachita, that hydrilla can never be eradicated once it infiltrates a lake.

"Our primary concern is around the swimming areas, the boat ramps, the marina areas and our recreation areas," says Richard Stokes, Lake Ouachita park manager for the Corps of Engineers.

"It's a lot worse on the west end of the lake, in the south fork of the Ouachita River," he said.

On the west end of the lake, a number of boat owners are starting to question why they're docked on Ouachita, if they can't get their boats out. There is growing concern they will pull up and go elsewhere, which would have a major economic impact on concessionaires and other businesses.

About 1,000 acres of the lake are affected by hydrilla. Stokes said controlling the weed has become one of his top five budget priorities, because of its aggressive nature.

Native aquatic plants cover about 6,000 acres on the lake, but Stokes said hydrilla will likely take over those areas in three years.

"The more funding, the more area we'll look at. Within the budget right now, 60 acres is about what we can top out, as far as what we can spend on this, because it's so expensive," he said.

Hydrilla cannot be controlled through drawdowns, like other underwater weeds. It is rooted, and can survive a freeze. Drawdowns actually give it an advantage over other native plants.

"The lake drops, you kill out the other stuff, and that gives this stuff even greater opportunity to grow," Stokes said.

The native plants have been around for about 20 years.

The Corps of Engineers has eradicated those plants, where necessary, around boat docks and other areas if they posed a nuisance, but those varieties didn't pose the threat of hydrilla, according to Stokes.

Stokes said he is trying to set up special funding for bio control measures, which could start as early as next spring but would take a decade to be established as a major control.

"You don't have the capability of sitting and watching it. You have to attack it. That's what's really got us concerned," he said. There's a hitch, while it may be the right time to attack the weed, the Corps of Engineer's budget was reduced this year and will be cut another 25 percent next year.

Stokes is scheduled next week visit Alabana's Lake Guntersville, which has had hydrilla for 11 years, and observe its control measures.

"That lake is 60,000 acres. Right now they're having to treat 14,000 acres for hydrilla.

Contrary to what anglers believe, Stokes says hydrilla is not good for fisheries because it can grow dense enough that game fish can't get into it. The fish they feed on get inside the cover and won't come out; the bigger fish can't get in it.

"The point I want to make to fishermen is that hydrilla is not beneficial to fisheries. If anything, it's very contradictory to that. It gets so dense they can't do anything," Stokes said.

We've had all this other stuff for 20-plus years that we've not had to really worry with it to a major degree," except around swimming areas and boat ramps, Stokes said.

"But this stuff, this hydrilla, I'm telling you this stuff is bad stuff. It will totally choke out almost the entire shoreline around this lake if not controlled," he said.

"We've had a tremendous amount of complaints on this stuff," Stokes said. "You cannot go through that stuff. I would let them show you an example, but I don't want to be stuck," he said during a water tour of the problem areas around Crystal Springs Recreation Area.

"You can see what we're dealing with on a small scale over just a three-year period. You figure in 10 years what it's going to be like," Stokes said, pointing out several small coves on the lake that are starting to get choked with the plant.

"You can't eliminate it," Stokes said the experts have warned. "It's kind of like crabgrass. You just don't get rid of it.

As the Corps of Engineers boat pulls into a cove near Crystal Springs Resort, Stokes says "This is what we're starting to find in a lot of areas around the lake." In the sunlight, the top of the water has a shiny, mottled appearance, where the tops of the weed are near the surface.

"The small coves are starting to get choked up with this hydrilla.

"If we don't do something with this cove, it will just continue filling all the way back out. And really you can't do anything with it, then," he said.

While herbicides are the immediate fix - spray hydrilla today, and the weed and all other plants are gone next week  You're talking 10 years before you see any major control" from bio measures, Stokessays.

"So for the next 10 years, if I am able to deal with this by next year, which I'm hoping to do, you're still looking 10 years out for the bio controls to take over," he said.

Bio controls include the hydrilla Pakistani fly, which is actually a very small gnat-like, leaf-mining fly.

When hydrilla surfaces, the fly lays its eggs on the plant, boring into the stems and leaves, stressing the plant enough to where it's not as invasive.

There's also a weevil, but it cannot reach the plant when it is under the surface, like the fly can. The weevil, unlike the fly, will migrate to other aquatic plants, but none that exist in this area.

It likely got into Lake Ouachita by hitchhiking on a boat or trailer from another lake, Stokes said.

That's another reason the Corps of Engineers is concerned with people pulling their boat out of Ouachita - infesting other areas. Some has already shown up on Lake DeGray.

"There's no silver bullet to this stuff. That's the sad thing about it,"he said.

Tips for stopping the spread of hydrilla From The U.S. Army Corps of Engineers is urging recreational boaters to not leave Lake Ouachita carrying hitchhikers of the aquatic variety.

The best way to stop the spread of hydrilla and other nuisance underwater weeds to other lakes is to be vigilant about cleaning equipment, according to the Aquatic Nuisance Species Task Force (ANS), an intergovernmental organization formed to prevent and control aquatic nuisance species.

Most frequent non-native aquatic weed problems in public waters throughout Akansas are hydrilla and alligatorweed.


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