Spiny Waterflea Discovered in Sandy Beach Lake, Iron County

Iron County, WI – June 2, 2025 – The presence of the spiny waterflea (Bythotrephes longimanus), a regulated NR40 species, has been verified in Sandy Beach Lake, located in the American Legion State Forest in Iron County, Wisconsin.

Initial evidence of the spiny waterflea was documented in the summer of 2023 by Zach Wilson, former Conservation Specialist with the Iron County Land & Water Conservation Department (LWCD). Wilson captured photographic evidence during routine lake monitoring efforts, which prompted further investigation.

In 2024, Wisconsin Department of Natural Resources (WI DNR) staff members Dara Filmore and Matt Boehlke were asked to conduct follow-up monitoring. Zooplankton tows were collected from the lake and sent to the Wisconsin State Lab of Hygiene. A quantitative analysis of the sample was performed by the lab. This allowed for confirmation of the presence of a single spiny waterflea, indicating that the current population density remains extremely low.

Spiny waterfleas are an aquatic invasive species known for their negative impacts on the aquatic food web. They reduce the abundance of native zooplankton available, which in turn reduces food availability for juvenile fish and other aquatic organisms. Zach Lawson, DNR Fisheries Biologist for Iron and Ashland counties, says that this is especially concerning for walleye and yellow perch in larval and juvenile stages, which are dependent on zooplankton for survival. Reduced food availability for these species can reduce growth rates and potentially impact overwinter survival rates.
At present, there is no effective strategy for controlling spiny waterflea; therefore, prevention and early detection remain the most critical approaches to prevent further spread. Here is what YOU can do to help stop the spread of spiny waterflea:

• Inspect and remove all aquatic plants and animals from boats, trailers, and gear. Never move live fish, plants, or water from one waterbody to another. Wipe all fishing lines clean.
• Drain water from live wells, bilges, and motors before leaving any waterbody.
• Rinse watercraft, trailers, and equipment with hot water when possible.
• Dry your boat, trailer, bait buckets, and other equipment thoroughly for at least 5 days or wipe down with a towel before moving to a new water body.

The Iron Co LWCD will continue to work with WI DNR to monitor throughout Iron County and evaluate strategies as necessary.

For more information about aquatic invasive species and what you can do to help, please visit https://dnr.wisconsin.gov/topic/Invasives/fact/SpinyWaterFlea.

Contact: Rayona Suelflow
Iron County Land & Water Conservation Department
Phone: 715-561-2234, ext. 1
Email: rsuelflow@ironcountywi.org
Website: ironcountylwcd.com