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Spiny water fleas new on the scene

September 22, 2009

What happens below the water's surface often goes unnoticed. That is not usually the case once aquatic invasive species invade. Beginning with only a few individuals, over time, aquatic invasive species spread, infestations worsen, and unfortunately are detected when it may be too late.

Last fall, anglers detected spiny water flea (Bythotrephes cederstroemi) in Great Sacandaga Lake in the southern Adirondacks. Spiny water flea had been known to be in Lake Ontario, but this was the first detection of it in an inland waterway in New York. In response, local groups mobilized to raise awareness among shoreowners, businesses, anglers and visitors about taking measures to reduce the risk of spread to other inland waters, including nearby Lake George, the Hudson River and Lake Champlain among others.

The good news? The Great Sacandaga community staffed seasonal stewards at public boat launches to talk with boaters and to inspect boats, trailers and gear for water fleas. The bad news? The stewards found water fleas attached to fishing gear and boats leaving the lake.

Article Photos

The buildup of spiny water flea on fishing lines can be so heavy that it becomes nearly impossible to fish.

Water fleas are not fleas at all and pose no health risk to humans; they are a tiny crustacean (less than half an inch long) with a long, sharp, spiny tail. Active from late spring thru late fall, spiny water fleas live from several days up to two weeks. They reproduce rapidly, and each female can produce up to 10 offspring every two weeks. As temperatures drop in the fall, eggs are produced that can lie dormant all winter. Eggs and adults are transported easily in bilge water, bait buckets and livewells and on fishing lines, downriggers, anchor lines and fishing nets.

Spiny water fleas threaten a lake's fishery as well as fishing itself. Water fleas eat small animals (zooplankton), including Daphnia, which are an important food for native fishes. In some lakes, water fleas caused the decline or elimination of some species of native zooplankton. Also, water fleas are not readily fed upon because their sharp spine makes it extremely hard for small fish to eat, which keeps the water flea population high. Their long, spiny tails also become entangled on fishing lines, creating havoc for anglers.

Native to Europe and Asia, the spiny water flea was first found in Lake Ontario in 1982 - most likely imported in ship ballast water. Since then, populations have exploded and are found throughout the Great Lakes and, now, inland waters too. Sadly, spiny water flea is not the only invasive to make its way from the Great Lakes to inland waters this year. Just last month, the bloody red shrimp (Hemimysis anomala) was discovered in Oneida Lake.

Prevention is the solution. All invasive species are difficult to control, but invasive animals are exceptionally difficult because they spread quickly and are tough to contain. Once detected in natural systems, they are usually impossible to eradicate. Preventing spread is critical. Do not let spiny water fleas tag along on your next fishing trip. Check for spiny water fleas and dispose on dry ground, and use high-pressure wash or water heated to 104 degrees to clean your boat and fishing gear after leaving your favorite lake and before entering a new one.

Keep spiny water fleas, bloody red shrimp, and other aquatic invasive species out of inland waters. Take part in helping to stem the tide of invasive species by making spread prevention measures part of the sport. Learn more about important steps to take at


Eye on Invasives is a biweekly column that spotlights a top invader when it is easiest to identify. The Adirondack Park Invasive Plant Program is a partnership program housed at the Adirondack Chapter of The Nature Conservancy in Keene Valley. Find out more about this award-winning program online at



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