Much Ado About Mussels

Post originally by Phil Moy, formerly Wisconsin Sea Grant; adapted by Sara Fox, UW-Extension

Dreissena polymorpha (zebra mussel) credit: Paul Skawinski for UW-Extension Lakes.

Zebra mussels have spread to more than 250 Wisconsin lakes and rivers since being first being identified in 1986. These small mollusks colonize docks, floats and boating equipment; their sharp shells can injure swimmers. They form dense colonies, up to 65,000 individuals per square foot, that can interfere with water supplies, disrupt food webs and alter ecosystems.

Like many other recent Great Lakes invaders, the zebra mussel is native to the Baltic region of Europe and was carried to our shores in the ballast water of ocean-going freighters. Zebra mussels were originally introduced to Lake St. Claire in the mid 1980’s. Since then, zebra mussels have spread throughout the Great Lakes region, into the Mississippi River, down to the Gulf of Mexico and into Canadian waters. They are spreading to inland lakes in many states including Wisconsin.

How Do They Spread? 

Zebra mussels are prolific breeders; a single female can produce tens of thousands of eggs annually. Eggs and sperm are released into the water column. After fertilization, the microscopic larvae, called veligers, float about in the water column for up to a month. At that time, the larval mussel transforms into a juvenile and settles to the bottom. Once settled, it adheres to a hard surface by means of sticky fibers called byssal threads.

Zebra mussels are able to spread easily due to the planktonic larval form and the adhesive adult form. The larvae can be carried in bilge water, live wells, bait buckets, or anything else that holds water such as dive gear. The juveniles and adults can attach to any hard surface that is submerged for a prolonged period of time including boat hulls, floats, anchors and lines, piers, swimming platforms, rocks, wood and vegetation. Adults are easily seen with the unaided eye; juveniles feel like sand or grit on the surface of boat hulls, motor or other submerged parts. Larval mussels can only be seen with a microscope.

The larvae need to remain wet to survive, but adults and juveniles can live out of the water for several days. A boat carrying adult or juvenile zebra mussels on the hull, larval zebra mussels in the bilge, live well water or plants tangled on the trailer can easily introduce zebra mussels from one lake to another.

Environmental Effects

Zebra mussels are filter feeders; they filter planktonic food from the water around them. Each zebra mussel can filter a liter (over a quart) of water per day. As they feed, they remove plant and animal plankton from the water. These tiny animals form the first food for the larvae of many desirable fish and are the food for other native species. As zebra mussels take plankton from the water, they compete with our native species for this food. The juveniles and adults can attach to any hard surface that is submerged for a prolonged period of time. Zebra mussels also make the water clearer. Though we often think of clear water as better water, clear water means there is less food for our native plankton-feeding organisms. Clear water also makes it possible for submergent vegetation to grow in areas that were previously too turbid to allow plant growth. This can contribute to weed-choked shorelines and changes in the food web and fish populations.

Zebra mussels adhere to the exterior of a clam.

Preventing the Spread

Lakes are usually identified as being colonized only after the mussels have been present for some time, perhaps years. People using boats, personal watercraft and diving in these and other waters may have unknowingly been vectors for the spread of zebra mussels into other lakes. Likewise, lakes not yet known to be colonized may already have zebra mussels in them. For this reason we need to take precautions to prevent the spread of zebra mussels and other invasive species every time we plan to move from one lake or river to another.


  • Drain water from bilge, live wells and motor.
  • Remove weeds from trailer, rudder, centerboard, anchor, motor and other areas.
  • Rinse mud from anchor and line.
  • Dispose of live bait.
  • Remove plant parts from the intake and run personal watercraft and jet boat engines for a few seconds out of the water.
  • Let boats, trailers and equipment dry for 5 days before moving to new waters.

As you pull docks, swim floats, anchors, lines and boats from the water, look and feel for zebra mussels on surfaces that were submerged through the summer season. Juvenile mussels may not be easily seen, but will feel like grit on the surface. Larger mussels are easily seen and may occur in groups or as separate individuals. If you find zebra mussels in a lake not known to be infested, save some of the specimens and please contact Wisconsin DNR, UW Extension or Wisconsin Sea Grant at the numbers below.

Other Invaders

Zebra mussels are not the only invaders trying to find their way into our inland lakes and streams. Recently, round gobies were found in Little Lake Butte des Morts near Lake Winnebago; the spiny water flea, a large predacious species of zooplankton, has been found in a handful of lakes in northern and southern Wisconsin. If these and other species find their way into our favorite lakes they may forever alter the ecosystem as they already have in Lake Michigan.

Round gobies are invaders like zebra mussels that threaten inland lakes.

The AIS Attack Pack

Wisconsin Sea Grant has developed a self-contained teaching tool for K-12 educators that can be checked out from the Wisconsin Water Library.

Contact Tim Campbell ( for more details.

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Passion and commitment of volunteers help protect lakes in western Vilas County

Emily Heald, Water Program Coordinator for the North Lakeland Discovery Center

In 2017, almost 200 volunteers in western Vilas County put in about 1,500 hours of time spent monitoring for aquatic invasive species, reviewing management plans, completing Clean Boats Clean Waters surveys at boat landings, and monitoring lake levels. It has all been a part of the 7-year partnership between the North Lakeland Discovery Center (a nonprofit environmental education center) and nearby towns of Manitowish Waters, Boulder Junction, and Winchester, as well as the Manitowish Waters Lakes Association and Winchester Town Lakes Committee. Our work consists of obtaining WDNR funding to create management plans on 24 lakes (spread over the years), with each project utilizing town financial donations and volunteer support for the matching funds required by the grants.

A proud group of folks from Winchester celebrate the CBCW program at a boat landing barbeque.

“We are hopeful that these projects will give us the knowledge and tools to ensure that we can prevent any potential invasive species contamination in the future through education and diligence by our lake property owners, as well as the recreational boaters and fishermen who visit the lakes.” (Gary Engstrom, Rock Lake)

For each project, multiple AIS identification trainings are held to give volunteers the skills to go out on their own time to monitor their lakes for AIS. Each project also holds at least two meetings open to riparian owners where results of studies are presented, and attendees learn about lake ecology.

We are creating a culture with lake property owners to be aware of, and routinely monitor, their lake and its environs.”(Rolf Ethun, Hiawatha Lake)

Some volunteers felt they were born into these projects from living on lakes their whole lives, while others join the cause through lake associations, after retirement, or by hearing about it through friends. However the sparked interest occurs, all volunteers overwhelmingly agree that it is “exciting and rewarding to see all the townships and lake associations work together” (Karen Dixon, Manitowish River) and “to see how everyone in the community has pulled together to solve the AIS problem” (Bob Becker, President of Manitowish Waters Lakes Association).

A lesson learned from this partnership? A little education can go a long way in “turning dock-loungers into caring citizen scientists-some a little and others a great deal” (Rolf Ethun, Hiawatha Lake).

Thank you to ALL of the volunteers who work together on these projects protect lakes and rivers.

Now, I’m hoping that working on invasive species issues I might be able to help leave an area be in better shape than I found it” (Greg Holt, Benson Lake).

Volunteers Al and Paul endure freezing temperature to monitor lake levels.


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Volunteers Defend Silver Lake

Paul Skawinski, UW-Extension Lakes

In, on, and around Silver Lake near Oconomowoc in the Village of Summit, Waukesha County, volunteers from the Silver Lake Management District are making a big difference. Through statewide programs like Clean Boats, Clean Waters and the Citizen Lake Monitoring Network, volunteers are collecting water samples, watching for aquatic invasive species, helping visitors check their boats for AIS before and after using Silver Lake, and removing Eurasian watermilfoil (EWM) through coordinated and carefully executed hand-pulling  events using snorkelers and SCUBA divers.

Silver Lake uses snorkelers and SCUBA divers in a coordinated effort to remove Eurasian watermilfoil from the lake. Credit – Paul Skawinski

Nearly 120 total hours were spent by eight volunteers staffing the boat landing on Silver Lake in 2017. The District also received a Clean Boats, Clean Waters (CBCW)  grant from the Wisconsin DNR, which provided 210 paid hours of watercraft inspectors at the landing. Invasive Species Committee Chair  Jessica Rice coordinates lake monitoring activities and enters the data into the state’s Surface Water Integrated Monitoring System (SWIMS) database. Her husband Nate Rice, Secretary of the Silver Lake Management District, discovered an unwelcome visitor at the lake’s boat landing in 2016 while conducting CBCW watercraft inspection and boater education. Nate discovered a fragment of a suspicious plant hanging from a boat trailer that was about to launch into Silver Lake. He removed this fragment, photographed it, and sent it for identification to Brad Steckart, Waukesha County Aquatic Invasive Species Coordinator, and Paul Skawinski, Statewide Coordinator of the Wisconsin Citizen Lake Monitoring Network. Brad and Paul agreed that the plant was starry stonewort, a prohibited invasive species impacting other lakes in the area, but NOT Silver Lake. Thanks to Nate being present at the landing, the imminent introduction of starry stonewort into Silver Lake was blocked. Frequent monitoring of the lake in 2017 discovered no evidence of starry stonewort established near the boat landing or elsewhere.

The District also collects information on water clarity, total phosphorus, chlorophyll-A, dissolved oxygen, and aquatic invasive species in Silver Lake. Again led by Jessica and Nate, this information helps track changes in the lake’s water quality. Monitoring the aquatic invasive species in the lake, especially EWM, allows the team to map the distribution of these species and execute targeted removal efforts. In lieu of herbicide treatments for EWM control, the District uses volunteer SCUBA teams and support watercraft to carefully remove these plants from the lake. In this way, they selectively remove the invasive plants and cause minimal disturbance to the lake and other nearby species. One former area of EWM infestation is now clear of the plant as a result of these manual removal efforts, and native plants have colonized the space instead.

Hundreds of lake volunteers across Wisconsin monitor water clarity trends by using a Secchi disc. Credit – Amy Kowalski.

Supported by the Wisconsin DNR, the Clean Boats, Clean Waters program, the Citizen Lake Monitoring Network, and the Waukesha County Aquatic Invasive Species program, Silver Lake’s volunteers are strong and committed to protecting their special lake. They remain vigilant and ready to detect changes in water quality or the arrival of aquatic invasive species. Unwelcome species do not go unnoticed, nor do the efforts of this amazing volunteer group. Silver Lake is in good hands.

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Hey anglers, be on the lookout for the fish no one wants to catch: round gobies

Post by Jenny Seifert, UWEX Aquatic Invasive Species Outreach Specialist

Round gobies are ferocious little bait stealers. For this reason, the Wisconsin Department of Natural Resources is calling on anglers to help the agency monitor whether these invasive fishes are spreading through the state’s waterways – if you happen to catch what you think is a goby, report it to WDNR.

Round gobies are an invasive fish known to steal bait and harm fisheries. Photo by Paul Skawinski

“We know gobies bite easily, so angling is a good way to capture them,” says Kendall Kamke, WDNR’s Oshkosh fisheries team supervisor, who oversees goby detection and control efforts in the Winnebago lake system.

The goby’s appetite for worms and other bait isn’t the only mischievousness that makes them an unwanted invasive species. They tend to eat the eggs and young of native fish and outcompete natives in their own habitat, thus threatening the existence of desirable fish and your enjoyment of catching them.

If you fish in the Winnebago system, look for this sign (and this fish!).

Since there is only so much the WDNR can do with minnow traps and nets, the help of anglers is critical to tracking whether these little bait snatchers are spreading throughout the state.

“This is our second year asking anglers to be our eyes and ears on the waters,” says Kamke.

A specific area of concern is the Lake Winnebago basin, where a couple of closed locks are the only things blocking the gobies’ passage from the Fox River into Lake Winnebago, an invasion to which would give them access to 17 percent of the state’s inland waters. If you fish in this area, you may have already seen the signs recruiting your help.

So what should you do if you catch a fish you suspect to be a round goby? First, look for their trademark features: fused-together pelvic fins that look sort of like a suction cup on their belly and bulging, frog-like eyes.

If your specimen has that resemblance, then report it to the WDNR using the online goby reporting tool, which you can access right there on the water, assuming you have a smart phone and decent cellular service. The tool walks you through a few simple steps that should take just a few short minutes to complete:

  • A mapping feature will help you report your location, an important piece of information that will help the WDNR follow up on your discovery, need be.
  • Take and upload a couple of photos of your specimen, one from the side and one of the belly to try to capture its distinguishing fused fin and frog eyes.
  • Be sure to include your name and phone number in case WDNR staff needs to contact you for further information.

Regardless of whether you report your possible goby on the scene or at home, the best thing to do, if possible, is take the specimen home with you in a plastic bag and bring it to your local DNR office to have it identified.

Fortunately, all of the reported goby sightings from Lake Winnebago have so far been misidentifications.

While the goby is a fish we hope you’ll never catch, your vigilance when fishing can be a big help in the state’s efforts to detect and control these bait thieves.

And, no matter what you catch, don’t forget to take the precautions to prevent the spread of aquatic invasive species before you leave the water: remove plants and debris from your boats and equipment, drain livewells and equipment and never move plants or live animals away from the waterbody.

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