Zebra Mussels Have Infiltrated The Red Cedar River System

The beleaguered ecosystem of Lake Menomin has developed another problem. This time it is an invasive species, zebra mussels (Dreissena polymorpha). Zebra mussels were found in Lake Menomin in the fall of 2023. And they were identified in Lake Tainter in the summer of 2024. Additionally zebra mussels have been located downstream of the Lake Menomin dam and in the Lower Red Cedar River. Zebra mussels are a small creature with a very high reproduction rate. They have the ability to drastically alter the ecology of the lake they invade.

Zebra mussels range in size from 1/8 of an inch to 2 inches. The adults have a “D” shaped shell with alternating light and dark strips. Hence the name zebra mussel. They live in colonies on hard structures in lakes, but they can also attach to plants. The mussels attach themselves to any hard structure in the lake including, sitting boats and motors, docks, water intake pipes, and clams.

Zebra mussels have a two-stage life cycle, It begins in the spring when the water reaches 54°. Each female mussel releases up to 1 million eggs into the water, while the male zebra mussel releases sperm. The spawning process results in around 25,000 new mussels. The first stage of a zebra mussel's life is a larval stage known as a veligers, which hatch 3 to 5 days after fertilization. The veligers float around the lake until they find a suitable structure to attach to with their byssal threads, which are strong root-like threads made of protein. The veligers can float around for a month in the water before finding a good place to bond to. The byssal threads are very strong so once the zebra mussels clamp onto a surface they are very difficult to remove. Zebra mussels live about 4 to 5 years. 

The massive number of larvae and later adult mussels can have many profound effects on lake ecosystems. In a limited number of lakes, zebra mussels actually increased the populations of some fish species while decreasing others. The mussels are omnivore filter feeders that eat both phyto and zooplankton, and each individual mussel filters about 1 quart of water per day. Due to their sheer numbers, the mussels can change water clarity, which in turn may allow some aquatic plants to thrive, and correspondingly the fish species that depend on these plants increase in population. Conversely, the zebra mussels filter out the nutrients other species of plants depend on., leading the plants and dependent fish populations to crash.

Multiple Zebra mussels attaching themselves to the same structure leads to many problems. Boats and motors can become inoperable if left sitting in the water. The mussels are able to clog water intake valves on boat motors and will slow down boats by attaching to the hulls. Native clams are desirable nestling places for colones of zebra muscles. Zebra mussels can kill off native clams by smothering the clams, as multiple mussels will attach to the clams shells making it impossible for the clams to feed. Zebra mussel shells can also cut the feet of swimmers and pets. 

A key question is how dense the zebra mussel population will become over the next few years. Wisconsin DNR Water Resource Management Specialist, Tyler Mesalk, described several factors which influence zebra mussel population densities. Zebra mussels prefer to attach to hard surfaces and since both Lakes Tainter and Menomin have soft and muddy bottoms this could be a limiting factor. Water chemistry plays a key role in determining zebra mussel population density. The most important elements of water chemistry are the amount of calcium in the water and conductivity that occurs in the lake. Calcium is needed by the zebra mussels to form their shells. Calcium is a positively charged ion atom. Conductivity is a measure of the ability of water to pass an electrical current. Conductivity in a lake can be measured with water meters. After determining conductivity, Mr Mesalk explains that the calcium levels in a lake can more or less be determined with some math. The good news is that both Lakes Tainter and Menomin are borderline suitable for zebra mussel growth. How much plankton the mussels will be able to filter out of the lake will also be a factor in the population growth. How healthy diet of plankton the zebra mussel will find the plankton in the two lakes is not known since the infestation is in its early stages. Of course a healthy diet of plankton will slow growth and poor diet will inhibit growth. 

Some of the factors in zebra mussel growth look promising for a limited infestation in both lakes, but nature is unpredictable so we wait and watch to see how bad the problem becomes over the next few years. 

At this point, the most important action lake users can do is to work to stop the spread of the zebra mussels. The Wisconsin DNR guidelines for stopping the spread of zebra mussels are as follows:

Prevention: The best way to keep a lake free of zebra mussels is to prevent their establishment. Wisconsin’s invasive species law prohibits the transport of aquatic plants, live animals, and water from a waterbody, with some exceptions for bait.

Before leaving the boat launch, conduct the following actions required by law:

• Inspect and remove aquatic plants and animals from boats and equipment.
• Drain all water from the boat and equipment.

Before entering another waterbody, conduct one of the following:

• Spray the boat and equipment with high-pressure hot water.
• Spray the boat and equipment with a ~500 ppm bleach solution (approximately 2 ½ tablespoons of household bleach (5.25% sodium hypochlorite) in 1 gallon of water) for 10 minutes.
• Allow the boat and equipment to dry out of water for at least 5 days.

Mechanical: Physical control options include benthic mats, manual removal, water level drawdown, and dredging. They may be effective at controlling zebra mussels at a localized site or structure; however, they are often expensive and can have negative impacts on native plants and animals. In addition, some of these physical control options may also require an approved permit from the DNR Waterways program.

Chemical: Several pesticidal control options have been developed, including copper compounds (EarthTec® QZ), the bacterium Pseudomonas fluorescens strain CL145A (Zequanox®), and potassium chloride (potash). However, due to the lack of documented long-term control efficacy, as well as the potential risk to non-target species, the Wisconsin Department of Natural Resources does not currently support the use of pesticides to control zebra mussels in lakes or rivers. Any product that claims to kill, control, repel, mitigate, or prevent zebra mussels would be considered a pesticide and must be registered with the Wisconsin Department of Agriculture, Trade, and Consumer Protection (DATCP). In addition, the proposed use of any pesticidal product in a Wisconsin waterbody would also require an approved Chapter NR 107 permit for the control of aquatic organisms.