Determining highest-risk vectors of spiny waterflea spread

Spiny water fleas are an invasive zooplankton that pose a serious threat to the ecology and recreational value of Minnesota’s waters. Previous studies have shown that over 40% of northern Minnesota lakes provide suitable habitat for spiny water fleas, and human recreational activity is believed to be the primary vector of spread. However, little is known about the specific pathways by which dispersal occurs. This can lead to unclear messaging and directions for recreationalists to prevent further spread.

To learn more about spread and prioritize prevention efforts, researchers measured the relative risk of spiny water flea attachment on commonly used recreational equipment including stationary anchor ropes, trolled fishing lines, trolled bait buckets, trolled downrigger cables, and trolled simulated livewells. Researchers sampled in the middle of the day and in the evening to account for spiny water fleas’ tendency to migrate closer to the water’s surface at dusk.

Researchers ranked the threat of each type of gear tested to help recreationalists prioritize their cleaning efforts in order to prevent further spread of spiny water fleas.


All research has been completed for this project. Researchers conducted 36 sampling events on Island Lake Reservoir (near Duluth, MN) and 36 sampling events on Lake Mille Lacs (near Garrison, MN).. Researchers compared the number of spiny water fleas on the deployed recreational equipment to the natural abundance of the fleas in the surrounding lake water. 

In total, researchers processed 216 anchor ropes; 72 bait bucket samples; 72 livewell samples; 72 downrigger steel cable samples; 72 downrigger fishing line samples (monofilament); and 216 shallow-running fishing line samples (72 monofilament, 72 fluorocarbon, and 72 braided). 

Researchers found that the downrigger and shallow-running fishing lines accounted for 87-88% of all ensnared spiny water fleas on the gear tested. They did not find a difference between twilight and daytime ensnarement of the fleas on gear. As expected, higher numbers of spiny water fleas in the lake water resulted in greater ensnarement of spiny water fleas on gear, particularly angling line. 

While few spiny water fleas were found in bait buckets or simulated livewell samples, these items are still risky because they can retain residual water in which the spiny water fleas could remain alive longer than on other gear. Residual water in any gear or boats carries this risk. 

Researchers found almost no spiny water fleas on anchor ropes. However, these ropes were left stationary in the water for several hours. They were not exposed to currents or flowing water. Researchers do not know if flowing water containing spiny water fleas would result in greater ensnarement of these fleas on anchor ropes. This is something that needs future research as researchers have received anecdotal reports of such ensnarement in invaded rivers and flowages. 

More detail: Researchers tested different types of angling line (fluorocarbon, monofilament, and braided), but there were not strong or consistent differences in the type of line. 


To reduce the risk of spreading spiny water fleas, researchers recommend that when fishing in infested lakes, anglers wipe down their line as they reel it in from their final cast of the day or as they reel in their downrigger line and cable. A small sturdy cloth or towel works well for this. 

At the dock, recreationalists should be very careful to drain all water from their boat and all gear and wipe out water holding areas such as livewells and bait buckets. From other studies, researchers know that spiny water fleas and their eggs cannot survive being completely dry for longer than six hours. Thus, researchers also recommend that all gear and the boat are dried in the sun until everything has been completely dry for more than 6 hours before moving to another water body. 

Project manager: Valerie Brady

Funded by: St. Louis County; Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources

Project start date: 2017

Estimated project end date: 2020