Using Triploid Grass Carp to Control Aquatic Vegetation

Invasive aquatic weeds can create major impacts on freshwater ecosystems. One of the primary reasons invasives are able to thrive, spread rapidly, and outcompete native species is that the environmental checks and predators that control these species in their natural settings are lacking in the ecosystems and habitat in which they become introduced.

The subsequent damages they cause occur on many ecological levels including competition for food or habitat (feeding, refuge, and/or spawning), direct predation and consumption of native species, introduction of disease or parasites, and other forms of disruption that lead to the replacement of the native species with the invasive species. As a result, invasives often cause serious harm to the environment, the economy, and even human health.

Some of the more commonly occurring non-native aquatic plant species that impact East Coast lakes, ponds, and reservoirs include curly-leaf pondweed, eurasian watermilfoil, hydrilla, and water chestnut.

The introduction of triploid grass carp to freshwater lakes and ponds can be an effective solution and natural alternative to managing and mitigating aquatic weed growth. When stocked at a proper rate, at correct sizes, targeting proper plant species, and the right time, triploid grass carp can reduce or eliminate the need for chemical treatment of the water to control aquatic vegetation.

Originally from Asia, grass carp have been imported to the United States since the 1960s to intentionally release into controlled freshwater environments for aquatic plant control. Grass carp, which rely almost entirely on aquatic plants for their diet, prefer to eat many of the non-native aquatic plant species that negatively impact freshwater environments, including the aforementioned pondweed species and watermilfoil.

Triploid Grass Carp in Woodridge Lake

Woodridge Lake is a beautiful 385-acre freshwater lake tucked away in the hills of Litchfield County, Connecticut. The lake, which is fed by the Marshepaug River, is a man-made resource, with a dam at one end that allows the level of the lake to be controlled.

Woodridge Lake Property Owners’ Association (WLPOA) closely monitors the lake, conducting water sample testing on a weekly basis. As with all waterbodies, the lake experiences aquatic weed growth, some years worse than others due to a variety of factors including climate change.

As a method to naturally mitigate aquatic weed growth, WLPOA plans to introduce triploid grass carp to the waterbody. A study by the Connecticut Agricultural Experiment Station states that grass carp is “the only biological control used successfully in Connecticut.”

Since the grass carp are an introduced species, only triploid grass carp, which are sterile, can be used. This eliminates the possibility that the stocked fish can reproduce and overpopulate the lake, or if any were to escape the lake they could not affect other waterbodies. As an additional measure of protection, to ensure that the carp remain in the lake, a screen, or emigration control device, is required. Princeton Hydro, in partnership with WLPOA, Rowledge Pond Aquaculture, and CTDEEP recently completed the installation of a carp screen.

The screen, which was custom designed by Princeton Hydro, is located in the outlet structure of the Woodridge Lake Dam, downstream of the spillway crest and within the concrete stilling basin of the spillway structure. Subsequently, the installation and operation of the carp screen will have no impact on spillway capacity or water surface elevations at the spillway crest. In addition, there will be no impact on the flow capacity or the water surface elevations of the Marshepuag River downstream of the dam outlet structure.

The emigration control device is a modular, vertical-bar screen composed of eight sections. A modular screen design was chosen to facilitate off-site fabrication and easier installation, as well as repair of an individual section, if necessary. Installed, all eight sections transect the entire 40-foot width of the spillway structure.

WOODRIDGE LAKE CARP EXCLUSION DEVICE DESIGN by Princeton Hydro

The carp screen was specifically designed to be easy to operate and maintain, minimizing clogging and facilitating easy cleaning from the downstream side of the screen during a range of flows. The operation and maintenance plan also consists of inspections every three months and precipitation-based inspections conducted by the WLPOA staff.

Overall, the use of grass carp will help Woodridge Lake manage aquatic weed growth in a natural way and maintain a healthy and vibrant lake environment for years to come.

To learn more about Rowledge Pond Aquaculture, the oldest private fish hatchery in Connecticut, go here: rowledgepond.com. For more information about Princeton Hydro’s lake management services, go here: bit.ly/pondlake.

Lake Management and Restoration in the Hudson River Valley

Lake Management Planning in Action
at Sleepy Hollow Lake and Truesdale Lake

The Hudson River Valley encompasses 7,228 square miles along the eastern edge of New York State. It comprises 3 million residents, 133 communities and 553 significant freshwater lakes, ponds and reservoirs. Princeton Hydro has worked with municipalities and organizations in the Hudson River Valley for over 18 years actively restoring, protecting and managing waterbodies throughout the area.

Princeton Hydro is currently implementing customized Lake Management Plans at two waterbodies in the Hudson River Valley: Sleepy Hollow Lake, a 324-acre drinking water reservoir/recreational lake located in Green County, NY and Truesdale Lake, an 83-acre lake in Northern Westchester County, NY.

Sleepy Hollow Lake

Stretching over two and a half miles long and reaching depths of approximately 70 feet, Sleepy Hollow Lake is a NYSDEC Class “A” drinking water reservoir that provides potable water for the Sleepy Hollow community. The lake is also extensively used by residents for swimming, boating and water-skiing. And, it is recognized as an outstanding large-mouth bass and white crappie (current New York State record holder) fishery!

Princeton Hydro was hired by the Association of Property Owners (APO) at Sleepy Hollow Lake to develop a comprehensive lake management plan. The first step involved an in-depth analysis of the biological, chemical and physical attributes of the lake, with the goal being to generate a database that can be used to better understand the interactions defining the Sleepy Hollow Lake ecosystem.

The data collection and investigation phase includes:

  • Watershed Investigation: an in-depth assessment of the major and minor tributaries and road network in order to identify areas of stream bank and ditch erosion; sources of both sediment and nutrient loading to the lake
  • Bathymetric Survey: the accurate mapping of water depths and the quantification of the amount of accumulated, unconsolidated sediment present in the lake
  • Fisheries & Food Web Study: the collection of fish and plankton data for the purpose of creating a comprehensive fisheries management program focused on managing the lake’s outstanding fishery, further promoting the ecological balance of the lake, and enhancing lake water quality
  • Aquatic Plant Mapping: the development of detailed maps identifying the plant species present in the lake along with their relative abundance and distribution throughout the lake, but especially within the shallower coves
  • Hydrologic & Pollutant Budget: the computation of the lake’s hydrologic budget and pollutant loading budget. The hydrologic budget represents the water balance of the lake and is an estimate of all of the inputs and losses of water. The pollutant budget represents an estimate of the amount of nitrogen and phosphorus entering the lake from various sources. These data are used to evaluate the effectiveness of lake management options, enabling us to determine the best, most ecologically sound and most cost-effective approach to protect and improve the lake’s water quality now and into the future.

Princeton Hydro is now in the process of utilizing all of the data developed during the investigation phase of the project to create a comprehensive Lake Management Plan that will be used to guide the APO’s future lake restoration and protection initiatives. The Lake Management Plan and supporting data will also be used by Princeton Hydro on behalf of the APO to seek grant funding for various lake and watershed restoration projects.

Princeton Hydro is also overseeing the aquatic plant management program at Sleepy Hollow Lake, the focus of which is to control invasive plant species in a manner consistent with and complimentary of the lake’s overall ecological enhancement.

Truesdale Lake

At Truesdale Lake, Princeton Hydro is working with the Truesdale Lake Property Owners Association (TLPOA) to develop a comprehensive Lake Management Plan. The Plan provides a detailed project implementation roadmap for TLPOA, including recommendations for priority ranking of particular activities and restoration measures. A key element of the Plan are the short-term (1-year) and long-term (5-year) water quality and problematic algae and invasive aquatic plant control goals. Another highlight of the Plan is the review of Federal, State, County and local grants, programs and initiatives that may provide funding for identified lake and watershed projects.

During the Plan’s development, Princeton Hydro has provided the TLPOA with lake management consultation services such as community education initiatives, the coordination of NYSDEC permitting activities associated with the implementation of lake restoration measures, and the oversight and administration of an aquatic weed management program at the lake.

Earlier this year, Truesdale Lake experienced excessive aquatic weed growth, which significantly reduced the water quality, recreational use and aesthetics of the lake. Princeton Hydro utilized its Truxor, an eco-friendly, amphibious machine, to cut and remove the nuisance weed growth from the lake. This program helped reduce the negative impacts to the lake and lake users caused by the dense weed growth. Future use of the Truxor to remove invasive weeds is already part of the long-term Lake Management Plan for TLPOA. The Truxor will be used in concert with other measures to control invasive weed growth and restore a more balanced native aquatic plant community.

For more information about Princeton Hydro’s work in the Hudson River Valley or to discuss your project goals, please contact us.