Last July, a new population of the invasive plant called the European frog-bit was found in Oconto, near Lake Michigan. Although this species is common in the coastal areas of Lakes Erie and Huron, its origins are in Europe and parts of Asia and Africa. The first spotting of the European frogbit in Wisconsin was at a nursery in 2018, and it was seen again in 2021 in Oconto. It’s assumed that the plant was transferred by long-distance boats, or from aquariums, where it is used decoratively.
The species grows in slow and shallow waters, often along lakes, swamps, rivers, and almost all other freshwater sources. It is “stoloniferous.” According to Ken Dolata of the Oconto County Land Conservation Department, this means the plant has “a horizontal stem that is located above the ground and usually produces adventitious [random] roots and vertical stems at the nodes.”
The leaves of the frogbit are leather-like and can grow up to two and a half inches long. This plant produces flowers that are heart-shaped and white, and can easily be mistaken for native species like the waterlily or water shield.
While the plant seems harmless, it’s detrimental to the aquatic environments it lives in. It grows in dense masses, blocking out sunlight, restricting fish and waterfowl movement, and decreasing dissolved oxygen levels that fish and other aquatic life need.
“The streams, wetlands, and drainages along the west shore of Green Bay are highly valued ecosystems for many fish species including Northern Pike, Yellow Perch, and many forage fish along with many species of birds, amphibians, and native plants,” says Dolata. “These species are all being affected by the presence of European frog-bit.”
Although just removing it from the water doesn’t appear to be difficult, European frog-bit is notoriously hard and expensive to contain and remove. Its fast rate of growth does not help the effort. It has been classified as an official noxious weed in Wisconsin and other parts of the United States.
The Wisconsin DNR is beginning to monitor the site and nearby bodies of water in an attempt to identify potential areas where the plant will spread. Removal started in the summer and fall of 2021 and has continued into this year.
[Sources: WBay.com ; Wisconsin Wetlands Association; Wisconsin DNR; Image Credit: Leslie J. Mehrhoff ]