Zebra Mussels

There are zebra mussels in Lake Winnebago, but testing of Becker and Round Lakes in 2009 showed no zebra mussels in those waters- yet! Let's keep it that way.

Zebra mussels are a tiny (1/8-inch to 2-inch) bottom-dwelling clams with a yellowish or brownish D-shaped shell, usually with alternating dark- and light-colored stripes. They can be up to two inches long, but most are under an inch. Zebra mussels usually grow in clusters containing numerous individuals.

Zebra mussels are the only freshwater mollusks that can firmly attach themselves to solid objects. They are generally found in shallow (6-30 feet deep), algae-rich water.

Zebra mussels usually reach reproductive maturity by the end of their first year. A fertilized egg results in a free-swimming larva called a 'veliger.' This veliger remains suspended in the water column for up to five weeks, and then begins to sink, eventually attaching to a stable surface (e.g., rocks, dock pilings, aquatic weeds, water intakes, boat hulls) on which to live, grow and reproduce. They attach to these surfaces with adhesive structures called byssal threads. Zebra mussels also attach to the shells of native mussels in great masses, smothering them.

Zebra mussels feed by drawing water into their bodies and filtering out most of the suspended microscopic plants, animals and debris. This process can lead to increased water clarity, but also to a depleted food supply for other aquatic organisms, including fish. The higher light penetration fosters growth of aquatic plants, and this thicker plant growth can interfere with boaters, anglers and swimmers. Zebra mussel infestations may also promote the growth of blue-green algae, since they consume other types of algae, but not the blue-green.

Financial impacts have been staggering for Wisconsin's water utilities and to power plants, where these animals congregate on and clog intake and distribution pipes. From 2001 through 2009, We-energies estimated that their control measures for zebra and quagga mussels and cladophora reached $28,429,000!

Once zebra mussels are established in a water body, very little can be done to control them. Therefore it is critical to take all possible measures to prevent their introduction.

No selective method has been developed that succeeds in controlling zebra mussels in the wild without also harming other aquatic organisms. To a limited extent, ducks and fish will eat small zebra mussels, but not to the point of effectively controlling their populations. As of yet, no practical and effective controls are known for control, emphasizing the need for prevention.

That prevention is to always inspect your equipment, boats, trailers, landing nets, decoys, and anything else that has been in the water. Remove any attached aquatic plants. Microscopic veligers and tiny zebra mussels can be hiding in the aquatic plants. Drain all water from all equipment, including the boat, boat trailer, boating or fishing equipment, including water in any bilge, ballast tank, bait bucket, live well or other container before leaving the launch. It's the law.