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The Daily Tar Heel

You've heard of Godzilla, now get ready for hydrilla

Above is a picture of the Riverwalk Greenway bridge near Weaver Street Market in Hillsborough showing the hydrilla infestation from May 2018. Treatment usually runs from mid-May to mid-August. Photo courtesy of Mark Heilman.

 An invasive species has been hurting the Eno River for years, but the Eno River Management Task Force is working hard to keep it under control. 

Hydrilla, a plant native to Asia, Africa and Australia, originally entered the United States for use in aquariums. It was first discovered in Lake Orange and has since spread to the Town of Hillsborough’s West Fork Eno Reservoir and throughout the Eno River. The state has applied the herbicide fluridone annually since 2015 to mitigate hydrilla’s spread, but this year might be the last year.

The task force is holding an open house Thursday at 6:30 p.m. to answer questions about the treatment program. 

Terry Hackett, the stormwater and environmental services manager for the Town of Hillsborough and a member of the task force, said hydrilla is not usually found in moving water systems like the Eno River. 

“It occurs all over the Southeast United States, specifically for the Eno River,” he said. “What makes it kind of unique is that normally you would find it more in ponds and reservoirs as opposed to moving systems.”

Hackett said the plant likely got into the Eno from Lake Orange and the West Fork Eno reservoir as pieces of the plant broke off and flowed downstream. 

“What’s really bad about the Eno is that, especially in the summer when it gets low, the hydrillas there just choke up the whole river,” he said. “It forms a complete mat.”

Caroline Choudhury, a senior environmental science major at UNC, is from Durham and grew up going to the Eno. 

“I volunteered with the Eno River Association in high school,” she said. “It’s a really great spot in Durham to get outside.”

Choudhury said she’s never experienced any of hydrilla’s negative impacts.

“I usually only go to the Eno in the winter, so I don’t know if that has an impact on growing times for this invasive species,” she said. “I also go to the Eno’s more populated areas where the river runs faster, like West Point. A bunch of people go there, so they might make an effort to control the invasive species better.”

Hydrilla’s presence has several impacts on the Eno River, Hackett said. It can prevent recreation, clog water intakes Hillsborough relies on, outcompete native plants and adversely impact the aquatic environment. To combat its growth, the task force turned to the herbicide fluridone. 

“Even though a lot of us were hesitant to go the chemical route, the treatment has worked very well,” he said.

Hackett said the cost associated with using fluridone is typically between $50,000 and $75,000 for two years. 

“The reason for the variability is it depends on the conditions of the river,” he said. “If the river is low-flow, we use less chemical so that the concentration isn’t too high.”

The task force is composed of local and state government officials from multiple departments. Hackett said the state pays for roughly half of the fluridone treatment.

“Invasive species are a big deal and a very costly impact to our local environment,” he said. 

The concentration of fluridone applied is within limits approved by the U.S. Environmental Protection Agency and poses no risk to swimmers, boaters or wildlife. Officials monitor chemical levels daily and can adjust them remotely, Hackett said. 

“They periodically come out on-site and make sure the battery and the cell signal and everything is working,” he said. “It’s a very technical system, but it works well.”

Hackett said the task force decided to continue treatment this year because hydrilla’s tubers, or storage organs, can remain dormant for up to seven years. 

“It’s been somewhat of a success story, given the fact that there are so many different agencies involved,” he said. “It’s sometimes hard to get a group like that focused, but we’ve been very focused and work well together.”

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