Lake Management for Aquatic Weeds – Hydrilla

Charlotte Water owns and operates two drinking water intakes as the water supply for our community; one at Lake Norman and another at Mountain Island Lake. Aquatic weeds can pose a nuisance to water suppliers at their drinking water intakes by clogging pumps or as a biological contaminant that must be treated. There are a variety of ways to manage aquatic weeds. Complete eradication is often impossible but suppression is achievable.

HYDRILLA

Hydrilla is a non-native aquatic plant that forms nearly impenetrable mats of stems and leaves at the surface of the water. Like many non-native species, Hydrilla crowds out other vegetation and grows rapidly. It was introduced in the U.S. decades ago as an aquarium plant but has taken over many water reservoirs nationally through accidental release. Its growing season is spring and summer; it is dormant mid-fall through the winter.

LAKE NORMAN & MOUNTAIN ISLAND INFESTATION STATUS

Though Hydrilla in local waterways has been managed for many years, annual biological controls have not been adequate to keep up with this season’s growth of the aquatic weed. Particular coves on Lake Norman are overwhelmed with the aquatic weed.

SUPPRESSION METHODS

Biological – Grass Carp

The typical method of managing Hydrilla in Lake Norman and Mountain Island Lake has been to stock coves with the Grass Carp fish. Periodically, tens of thousands of Grass Carp are released so that they may digest Hydrilla and keep the aquatic weed suppressed. The last batch of carp was released into Lake Norman in May 2018 in partnership with the Lake Norman Marine Commission, Duke Energy, Charlotte Water, and the NC Department of Environmental Quality (DEQ) in consultation with the NC Wildlife Resources Commission.

Chemical – Aquatic Herbicide

Specially formulated herbicides designed for application in water may also reduce the Hydrilla infestation. For herbicide application to be most effective, it must occur during the growing season (spring, summer) and by a licensed pesticide applicator.

Physical – Machinery Dredging

Machine dredging of the lake bottom is possible, but Hydrilla grows to depths of approximately 10 feet. Due to the cost and likely subsequent erosion, the use of heavy equipment to dredge or rake Hydrilla is not suggested. Also, mechanical control of Hydrilla only provides temporary relief and likely spreads the weeds to other areas of the lake through the release of plant fragments.

UPCOMING MANAGEMENT ACTIVITIES

At this time, Charlotte Water, Duke Energy, the Lake Norman Marine Commission, Charlotte-Mecklenburg Storm Water Services, and NC Department of Environmental Quality are relying on increased biological methods to suppress the weed. The group plans on releasing additional Grass Carp fish in the spring.

This method takes time but can be effective. In addition, the growing season for Hydrilla ends in the early fall, and the weed will go dormant.

We are encouraging residents to give the Grass Carp fish the time they need to ingest the weed.

In order to determine the number of Grass Carp fish that will be released in the spring, researchers at NC State will be surveying Lake Norman in the next couple of months to get an accurate acreage of Hydrilla.

FAQs

Can I apply an herbicide in waters adjacent to my property?

If residents plan on applying an herbicide please contact a qualified, licensed aquatic applicator to apply an herbicide approved by the EPA for use in aquatic settings. Please note that stakeholders from Charlotte Water, Duke Energy, the Lake Norman Marine Commission, Charlotte-Mecklenburg Storm Water Services, and NC Department of Environmental Quality do not advise property owners use this method.

What steps will be taken to protect the community from any negative impacts of applying the herbicide?

If property owners use herbicides, Charlotte Water is requiring all applications of herbicide be applied at least one quarter mile away from drinking water supply intakes. The herbicide used should be approved for use in aquatic situations to protect aquatic life in the area.

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