Carp to curb invasive weed at Lake Mooney

Stafford County says it’s going to use fish to attack its growing aquatic weed problem.

Hydrilla, an aquatic weed, is a problem for many bodies of water in Stafford County, including the 520-acre Lake Mooney resorvoir. Stafford County officials are implementing a recommendation of the Virginia Department of Game and Inland Fisheries (DGIF) to introduce white amur or “grass carp” into Lake Mooney to help combat the issue. Because of hydrilla’s high growth rate, it can quickly take over a water body and impede recreational activities and aquatic habitats. To ensure the establishment of the newly introduced population of fish and to give the fish time to manage the weeds effectively, Stafford County asks residents to release these fish, if caught.

Hydrilla is proliferating at Lake Mooney and has the potential to create a serious issue, particularly along the shoreline. Listed as a federal noxious weed, hydrilla is a perennial aquatic plant that looks similar to the herb thyme and is found in many freshwater habitats around the world, according to Stafford County officials. This plant can grow up to 30 feet long and has a growth rate of up to one inch per day, officials say.

Introducing grass carp, a type of herbivore fish, is a more environmentally friendly move as well as a more economical solution. The advantages of using grass carp to manage aquatic weeds include constant feeding activity against growing weeds, low costs and longevity of the maintenance method once it has become established.

Carp must be stocked in sufficient numbers so that their consumption rate exceeds the growth rate of the plants to remove aquatic weeds. John Odenkirk, a biologist with DGIF, will help the County determine the number of grass carp needed, per acre, to keep hydrilla at an acceptable level while also allowing native vegetation to survive. Again, to help a successful establishment of the fish, residents are asked to release any carp they catch while fishing, Stafford County says.

Their coloring identifies these fish: an olive green or dark gray hue on top with a light gold or pale yellow side. Their belly is silver and their fins are light green or gray. They also have unusually large fish scales. The carp introduced into Lake Mooney in May 2020 will be 10 inches long. Carp can grow up to four feet long and have an average life span of 10 years, officials say.