06/01/2026
U.S. Fish and Wildlife Service (Service) personnel will apply lampricides to Cass River (Saginaw and Tuscola Counties) to kill invasive sea lamprey larvae burrowed in the stream bottom. Applications will be conducted between June 2nd – June 11th, 2026, in accordance with State of Michigan permits. Application dates are tentative and may be changed based upon local weather or stream conditions near the time of treatment. For more information on sea lamprey control in the Great Lakes visit fws.gov/invasive-sealamprey. Sea lampreys are parasitic fish native to the Atlantic Ocean that invaded the Great Lakes via shipping canals in the early 1900s and remain a major threat to the fishery. They attach to fish with a suction-cup mouth lined with sharp teeth, feed on their body fluids and can kill up to 40 pounds of fish during their parasitic phase. Each spawning pair produces up to 100,000 eggs, with larvae living for years in tributaries before transforming into parasites that migrate to the Great Lakes to prey on host fish. Infested tributaries must be treated on a regular basis with lampricides to control sea lamprey populations.
Failure to reduce sea lamprey larvae populations in streams will result in significant damage to the Great Lakes fishery. Extensive preparations and precautions are required to deliver a safe and effective stream treatment. Prior to treatment, trained personnel collect data on stream water chemistry and discharge. In addition, they may conduct on-site toxicity tests and streamflow studies using non-toxic dyes that make stream water appear red or green. Lampricides are carefully metered into the stream for approximately 12 hours and continually analyzed at predetermined sites to ensure proper concentrations are maintained as they move downstream. Applicators are trained and certified by regulatory agencies for aquatic pesticide applications. The U.S. Environmental Protection Agency and Health Canada Pest Management Regulatory Agency have reviewed human health and environmental safety data for lampricides and concluded that the lampricides pose no unreasonable risk to the general population and the environment when applied at concentrations necessary to control larval sea lampreys. However, as with any pesticide, the public is advised to use discretion and minimize unnecessary exposure. Lampricides are selectively toxic to sea lampreys, but some fish, insects, and broadleaf plants are sensitive.
The sea lamprey control program is contracted through the Great Lakes Fishery Commission (Commission) to the Service and Fisheries and Oceans Canada. Established in 1955 by the U.S. and Canadian governments, the Commission began chemical control of sea lampreys in 1958 as a response to the catastrophic damage of their invasion. Since that time the highly successful program has contributed significantly to the maintenance of the $5.1 billion Great Lakes sport and commercial fisheries. For more information on the Commission, visit www.glfc.org. The Service works closely with the U.S. Geological Survey to support research, such as the development of supplemental control techniques to be used in areas where lampricides are particularly challenging to apply. In addition, the Service maintains a partnership with the U.S. Army Corps of Engineers in developing a comprehensive barrier strategy for sea lampreyproducing streams, and is investigating barrier design, traps, attractants, and biological control as part of a robust research program administered by the Commission. For additional information in Canada call 1-800-553-9091. To reach the Marquette Biological Station call 1-906-226-6571 or to reach the Ludington Biological Station call 1-231-843-7300.
