Invasive species are one of the leading threats to native wildlife. Approximately 42% of Threatened or Endangered species are at risk primarily due to invasive species. Unwanted invasive species could have a devastating effect on our ability to enjoy the lake, our health and our housing values.

What makes a species invasive?

An invasive species can be any kind of living organism—an amphibian, plant, insect, fish, fungus, bacteria, or even an organism’s seeds or eggs—that is not native to an ecosystem and which causes harm. They can harm the environment, the economy or even, human health.

Species that grow and reproduce quickly, and spread aggressively, with potential to cause harm, are given the label of “invasive.” An invasive species does not have to come from another country. For example, lake trout are native to the Great Lakes, but are considered to be an invasive species in Yellowstone Lake in Wyoming because they aggressively compete with native cutthroat trout for habitat.

Aquatic Invasives

Plants and animals that are not native to a waterbody are termed aquatic invasive species (AIS). They are harmful because they grow in large numbers or densities and may displace native plants and animals while harming the balance of ecological processes, water supply, recreation and other water uses.

AIS are not a new problem, but they are a growing problem. There have been 179 known exotic plants and animals noted in the Great Lakes alone. Florida also has long been known as a gateway for AIS introductions, and has experienced hundreds of new species over the last century.

There have been many other AIS introductions on smaller scales in many other parts of North America. The common carp was introduced intentionally, thinking it would be a good food source. Purple loosestrife, water hyacinth, water lettuce were popular ornamental plants. Some AIS were introduced to get rid of other AIS, compounding the problem!

National and international programs to curb AIS introductions are largely inadequate and ineffective. This means that state and local programs must take the lead in solving their local Issues and concern. SMLA works with Virginia Division of Wildlife Resources (DWR), and The Tri-County Lakes Administrative Commission (TLAC), APCO and other technical expert advisors and SMLA members to deal with the various issues of AIS at SML. All stewards and users of SML must be aware of and pull together to limit the introduction and harm of AIS.

Aquatic Non-Native Invasive Vegetation

There are numerous types of aquatic vegetation that have been observed growing in SML. The most aggressive non-native aquatic weed is hydrilla, followed by brittle naiad. Certain pondweeds are also invasive such as curly-leaf pondweed. Native weeds include water willow, chara (muskgrass), sago pondweed,  common elodea, southern naiad, coontail, nitella, longleaf pondweed, fragrant water lily.

Filamentous green algae can accumulate on rip rap and swim ladders but it is native.

Prior to  2013, aquatic weeds were very widespread particularly in the Bull Run and Blackwater portions of the lake. Many efforts to control the weeds were undertaken by TLAC and APCO including the use of herbicides.

The management plan settled upon by TLAC was the release of sterile grass carp which consumed all weeds in the lake, even the native ones. These fish were expected to live about 10 years, and consequently the weeds are expected to repopulate the historic areas where they were originally an issue. Re-introduction of weeds from other waterbodies, as well as a robust seed bank in the lake sediment will also lead to more weeds.

TLAC, a county-run agency, makes management decisions regarding weeds with the assistance of the DWR, county representatives, APCO and other advisors such as SMLA.

Annual surveys are conducted by APCO and SMLA at historic weed areas as well as new weed beds reported by residents. The surveys determine the acreage impacted as well as species of weeds and guide how TLAC will respond.

TLAC operates with an Aquatic Vegetation Management Plan which guides how and when responses to weed growth are planned each year. The management plan focuses on the use of grass carp as the most cost effective and least environmentally disruptive approach to weed control. Herbicides and mechanical weed harvesting are not currently part of any management plan.