What are Aquatic Invasive Species (AIS)?Aquatic invasive species (AIS) are organisms, such as plants, animals, and pathogens, that can be transported by contaminated water from outside their native range. They have the potential to cause significant harm to native aquatic ecosystems as well as economic and recreational impacts to places like Lake Roosevelt National Recreation Area. 
NPS Photo Why should we be concerned about AIS?Aquatic Invasive Species lead to significant impacts, economically, recreationally, and ecologically. For this reason, boaters should not only be concerned about AIS, but also aware of the responsibilities it takes to prevent AIS. Economically, AIS cause impacts to hydropower and water systems. When organisms accumulate on wet surfaces (also known as biofouling), they clog hydropower facilities, irrigation canals, and water pumps. Fish hatcheries also suffer from infestations of invasive species. AIS ultimately costs taxpayers hundreds of millions of dollars a year due to their ability to spread throughout bodies of water. Recreationally, AIS leads to closures of boating opportunities. Docks, beaches, and boats become encrusted by AIS. Invasive species hitch rides on boats, trailers, fishing gear, waders, and even seaplanes, leading to continued spread between bodies of water. Shorelines on beaches are harder to access, and swimming is impacted by large quantities of algae. Ecologically, native species can by impacted by AIS. Native fish, invertebrates, plants, and waterfowl struggle in the presence of AIS; the invasive species take over native habitat, outcompete, and even reduce native populations. Reduced native fish populations also impact recreational fishing opportunities. Water quality can also suffer in the presence of AIS. Nutrient levels are affected by AIS, leading to a less productive ecosystem in Lake Roosevelt. Toxic algal blooms dominate ecosystems by changing water quality and releasing toxins into the water. What kinds of AIS do we have at Lake Roosevelt?
©2024 Gabriel Campbell Eurasian watermilfoil (Myriophyllum spicatum)Eurasian watermilfoil is an invasive aquatic plant that grows underwater, mainly in freshwater ecosystems. It can handle changes in salinity, acidity, and temperature, making it very adaptable to its environment. It grows in dense formations which covers up native aquatic plants and prevents them from having access to light. It can outcompete native species, ultimately leading to flooding areas and clogging water intakes. Eurasian watermilfoil can spread quickly and creates poor habitat for other aquatic organisms. Eurasian watermilfoil can be easily identified by its 1-1.5 inch leaves in whorls of four around the stem. It typically has between 14-21 leaflets per leaf, which is a key identifier of this aquatic plant. 
©2021 W. Juergen Schrenk Flowering rush (Butomus umbellatus)Flowering rush is an invasive aquatic plant that grows along shorelines in lakes, rivers, and wetlands. Like Eurasian watermilfoil, it outcompetes native plants, creating dense patches throughout the ecosystem. This in turn destroys native habitat for animals that depend on the native plants as a food source and shelter. Thick growths of flowering rush can clog canals, irrigation drainages, and cause flooding. Additionally, it serves as a home for the great pond snail that hosts a parasite responsible for swimmer’s itch. Dislodging, or pulling, this plant out of the water is actually harmful by allowing the plant to float downstream and invade other parts of the lake. If you come across flowering rush, take a photo and report rather than dislodging the plant. This aquatic plant can survive on shorelines and up to 20 feet of depth in the water. It can be identified by its 20-50 pink flowers that form in a cluster at the end of each stalk. 
USFWS Ryan Hagerty Northern Pike (Esox lucius)Northern pike are an introduced species of fish that are native to parts of the mid-west United States and Alaska. This invasive fish can potentially grow up to 50 inches over 20 years. They aggressively prey on other native fish leading to significantly reduced populations. This can change the ecology of the entire lake. Additionally, one female can lay up to 250,000 eggs, causing a quick population growth. The Colville Confederated Tribes offers a bounty program for Northern pike at $10 per fish head turned in, creating incentive to reduce the number of Northern Pike in Lake Roosevelt. Learn more about the invasive fish species at Lake Roosevelt. 
© Environment Agency 2011 Northern Crayfish (Faxonius virilis)Northern crayfish (also known as the virile crayfish) is an invasive crustacean to Lake Roosevelt, but native to Montana, Wyoming, the Great Lakes, the upper Mississippi River, and the Hudson River. They were likely introduced as a form of bait by anglers to this area. They can grow up to 5 inches long and are generally light brown with dark markings on their abdomen. Invasive Northern crayfish have bumpy claws while signal crayfish have smooth uniform brown claws with white markings. As an invasive species, Northern crayfish are actively outcompeting signal crayfish, the only native crayfish in Washinton. In order to combat this, Washington state has an open crayfish fishing season is from the first Monday in May through October 31. Catching Northern crayfish allows anglers to help reduce this AIS population in places like Lake Roosevelt. Learn more about invasive fish species at Lake Roosevelt. 
Credit Leslie Mehrhoff, Bugwood.org Asian Clams (Corbicula fluminea)Asian clams are small freshwater mollusks that are invasive to Lake Roosevelt, but native to southern Asia, Australia, and the eastern Mediterranean. They were found along the Columbia River in Washington State as early as 1938. Asian clams cannot attach to surfaces like zebra or quagga mussels do using byssal threads, but they can be found in still water and throughout boating gear. Asian clams change the nutrient levels in water, leading to dense toxic algal blooms which makes swimming and boating along the water uninviting. They can be identified as brown to golden color and between 0.25 to 1 inch in size. Larval forms are microscopic which is how they can be transported between water bodies so easily. They are often found on or just below the surface of sediment. What kinds of AIS are we trying to prevent at Lake Roosevelt?
NPS / Schaeppi Quagga and Zebra Mussels (Dreissena bugensis and Dreissena polymorpha)Invasive quagga and zebra mussels are the primary species we are trying to keep out of Lake Roosevelt. They are small freshwater mollusks that can latch onto hard surfaces with strong fibers known as byssal threads. These mussels can then clog boat intakes, irrigation systems, and even hydroelectric power facilities. Microscopic larvae can be easily transported from one body of water to another. Quagga and zebra mussels are native to Ukraine and Russia but were brought to the Great Lakes from unregulated ballast waters in ships from the Caspian and Black Seas. Since arriving to the United States, they have spread incredibly fast via recreational boats. In 2023 and 2024, quagga mussels were identified in the mid-Snake River and in the Twin Falls area respectively. The Snake River in Idaho flows into the Columbia River. Rapid response and sampling were initiated after the quagga mussel discoveries, and monitoring will continue due to the severity of this AIS. It is now even more critical that mussels are spotted before they become a problem. Both quagga and zebra mussels can be identified by their byssal threads, which allow them to attach to hard surfaces. Quagga mussels are rounded, have narrow stripes, and are usually light tan to white in color. Zebra mussels are more triangular in shape and can have stripes or zig-zag patterns in a variety of colors. Native mussels are generally much larger in size and do not have the ability to attach to hard surfaces. 
© evolvulux / Photo 48647486 / 2019-05-31 / iNaturalist.org / CC-BY-NC New Zealand Mud Snail (Potamopyrgus antipodarum)Invasive New Zealand mud snails are an incredibly small (0.125 inches) aquatic snail that is extremely adaptable to various climates and water types, making them another target AIS we are trying to avoid at Lake Roosevelt. They can dominate water bodies by creating very dense patches that are hard to eliminate, outcompete native aquatic snails and insects, and disrupt food chains that can lead to lower fish populations. New Zealand mud snails have been found in the Snake River in Idaho and in other parts of the Columbia River. New Zealand mud snails are identified by five or six whorls on their shell. When looking at the snail with the point of the shell facing upward, the opening of the shell will be on the right-hand side. What can we do about AIS?
NPS Photo Lake Roosevelt is currently free of quagga/zebra mussels and New Zealand mud snails. In order to keep Lake Roosevelt free of harmful AIS, it is critical that all boaters do their part. You can help by keeping Lake Roosevelt’s waters clean by following the steps below every time you leave a water body: Clean, Drain, Dry
If your boat has been in waters with confirmed or suspected AIS (such as Lake Mead, Lake Mohave or Lake Powell) within the last 30 days please call the Washington Department of Fish and Wildlife AIS hotline at 1-888-WDFW-AIS. 
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Last updated: January 6, 2025