Spiny and Fishhook Waterflea
Spiny (Bythotrephes longimanus) and fishhook (Cercopagis pengoi) waterfleas are small predacious crustaceans that threaten aquatic ecosystems and fishing by competing with native fish for food and fouling gear. Both arrived in ships' ballast water from Eurasia. Spiny waterfleas were discovered in Lake Ontario in 1982, then spread to all of the Great Lakes and some inland lakes. Fishhook waterfleas were first discovered in Lake Ontario in 1998, then spread to parts of lakes Michigan, Erie, and the Finger Lakes of New York.
Anglers often discover new infestations. Both waterfleas collect in masses on fishing lines and downrigger cables. These masses can clog the first eyelet of rods, damage a reel's drag system, and prevent fish from being landed. They can spread to inland waters when fishing gear is contaminated with egg-laden females. While females die out of water, under certain conditions they produce eggs that resist drying, remain viable, and can establish a new population. Eradicating established infestations is impossible. Your help detecting and reporting new infestations is vital for preventing their spread.
Identify Invasive Waterfleas
- Difficult to distinguish without magnifaction 1/4-5/8 inches (5-15 mm) total length
- Clumps look and feel like gelatin or cottom batting with tiny black spots
- Prefer deep lakes, but can establish in shallow waterbodies and rivers
- Abundant during summer (June-September) depending upon water temperatures
What You Can Do
- Learn to recognize these waterfleas on fishing gear.
- Inspect and remove aquatic plants and animals, including gelatinous or cotton batting-like material from lines, especially where they meet a swivel, lure or downrigger ball connection (plucking like a guitar string helps).
- Drain lake or river water from livewell and bilge before leaving access.
- Dispose of unwanted live bait and worms in the trash.
- Report new sightings - note exact location; wrap a plant fragment in a wet paper towel, place in a sealed plastic bag; and call Minnesota Sea Grant Program in Duluth, (218) 726-8712, or the Minnesota Department of Natural Resources in St. Paul, 1-888-MINNDNR or (651) 259-5100, or a local DNR fishery office.
Know the rules!
Specimens are needed to confirm sightings, but some jurisdictions prohibit possession of invasive waterfleas and other aquatic animals and plants. Contact your local natural resource management agency for instructions. Unauthorized introduction of fish, crayfish, or plants into the wild is illegal. Protect your property and our waters.