The Lake Where You Live

It seems the invasive species just keep coming. We get one or two under control, and another one shows up on the state’s watch list or in an actual infestation.

Three water plants have come to my attention lately, two from Michigan and one here in Wisconsin. Let’s start with our neighbor to the east.

Water primrose has made it onto the watch list in Michigan. It can prosper and spread in shallow water, such as in wetlands and along lake shorelines. It grows rapidly, and with its upright stems and horizontal runners it can form dense mats and crowd out native water plants. 

Like many invasives, water primrose is quite appealing to the eye, with showy yellow flowers that have five or six petals. You might see it floating on the surface or as an emergent (standing above the surface) along the water’s edge. The stems are reddish, the leaves dark green and elongated. The plant can grow up to two feet tall. 

In the United States the plant is native to the southeastern states. In Michigan it was first spotted in 2018 in the Detroit International Wildlife Refuge in Wayne County, and since then infestations have been found in three other counties.

Also in Michigan, European frog-bit has been removed from the watch list, not because it has disappeared but because it is now considered established. The plant can form dense surface mats in slow-moving waters like backwaters and wetlands. It can impede boat traffic and change the food web and habitat for ducks and fish. It thrives best in waters that are rich in calcium and have no wave action.

Frog-bit is often spread to new water bodies when plants or turions are transported on boats, trailers and recreational gear: hunting is considered a high-risk pathway for spread. The plant is mostly free-floating but can take root in shallow water. It has small round to heart-shaped leaves with purple-red undersides, configured in a rosette. The single flowers have three white petals and a yellow center. The plants are said to resemble small water lilies. 

Native to Europe, Asia and Africa, frog-bit has been found in Michigan, New York, Ohio, Pennsylvania, Vermont and Washington. 

As for the Badger state, I recently learned of two growths of arrow arum in two lakes in Bayfield County, reported by AIS coordinator Andy Teal at the Bayfield County Lakes Forum annual meeting. 

This plant is native to Florida, found in swamps and marshes and along muddy lake and stream shorelines. It can be mistaken for the common native arrowhead plant, although its leaves are much larger — usually about 10 inches to a foot long and half as wide, but in some cases up to twice that size. 

The leaves cluster on long, succulent stalks up to three feet long. The flowers are small and light yellow on a finger-like spike. According to Teal, arrow arum can be removed manually if detected early but becomes very difficult to control if allowed to spread and become well established.

These plants are cases in point about the need to be vigilant for invasive species and to take proper care to avoid moving them to additional waters.

Ted Rulseh is a writer, author and lake advocate who lives on Birch Lake in Oneida County. His new book, “Ripple Effects,” has been released by UW Press. You can learn about it by visiting his website at https://thelakeguy.net.