The Huron River watershed has many exotic and invasive plant species that have drastically changed our lake, river, and riparian ecosystems. These plants grow quickly, spread quickly, alter habitat for the indigenous creatures and plants, and reduce recreational benefits for humans. Once invasive plants become established, it is often too late to eradicate them from an ecosystem. Finding the plants early is key to protection, which means both scientists and volunteers need to get boots on the ground and boats in the water to look for them! 

The Midwest Invasive Species Network (MISIN), run by Michigan State University, is a great resource for spotting when invasive species arrive in a new area. Users can install the MISIN app on their mobile devices to report findings, and the network also holds data collected by government employees and scientists. Of course, the breadth of the mapped data depends on where people are looking and when they choose to report their finds. 

A tour of the problem 

Frog bit (floating) and Phragmites (background). credit: Oakland County CISMA

 Let us take an exotic invasive plant tour of the Huron River system via the MISIN mapping software, starting at the river’s estuary near Lake Erie, and heading upstream to its headwaters in Springfield Township. At the river’s mouth, the two most reported plants are European frogbit and phragmites. European frogbit is a relatively new invader to the river system. This small floating plant resembles lily pads, but the leaves are tiny, measuring just 1/2 – 2 1/2 inches. The plant forms dense mats that can impede boat traffic and alter food and habitat for waterfowl and fish. Frogbit has also been found in Novi-area detention ponds right on the Huron’s eastern border, but otherwise has not been found in the Huron River watershed.

Flowering Rush. credit: Michigan Sea Grant

As the tour navigates the downriver area and makes its way up to Belleville and Ford lakes, phragmites and flowering rush are plentiful, and they remain so throughout the Huron system. Both are riparian plants, meaning that they are on the edge of the river or in very shallow water. Phragmites is a very tall perennial reed (8-10 ft) that spreads very easily, very thickly, and dominates areas, preventing other plants from establishing themselves. Flowering rush is another type of perennial reed that does not grow as tall (1-4 feet) but, like Phragmites, grows in very thick stands that prevent bird and amphibian habitat and impede water access.  

As the tour continues up the river, a different species of aquatic exotic invasive plants is found. Ford and Belleville Lakes make a nice home for Eurasian watermilfoil, an infamous plant that clogs up lakes and will even clog up the boat motor of anyone who attempts to plow through it! 

Eurasian Watermilfoil. credit: Scott Brown

Going upstream through Ypsilanti and Ann Arbor, phragmites, flowering rush, and a smaller amount of purple loosestrife (another pretty, yet problematic riparian plant that grows in monoculture stands) remain the primary problems.  

Graham Battersby, HRWC volunteer, surveyed Barton Pond for water clover in 2015. credit: G. Battersby

In the Argo and Barton impoundments, we meet another floating plant, the European Water Clover. This exotic invasive was probably released from someone’s aquarium and now grows in patches in these two ponds. Water clover looks just like a four-leaf clover and floats on the surface, forming dense vegetative mats. Thankfully, it seems that water clover does not spread through running water. HRWC and the State of Michigan have been monitoring this stand of water clover and have not yet seen it spread downstream or upstream from Argo and Barton. 

Starry Stonewort: Closeup. credit: Scott Brown

The tour continues upstream from Barton Pond, past Dexter, and up to the Chain of Lakes area. The Chain of Lakes region is a series of mostly natural lakes in line with the river and is where starry stonewort starts to become very problematic. These plant-like algae are present from here up to the headwaters in all the inline lakes. Like the other invasive species, the problem with starry stonewort is that it grows very dense. What makes starry stonewort probably worse than other plants like Eurasian water milfoil is that no treatments exist that reliably remove it. Copper-based herbicides can cause a temporary die-back, but these chemicals harm the rest of the ecosystem as they indiscriminately kill non-target plants and smaller organisms like macroinvertebrates. Starry stonewort is a relatively new plant on the scene, and there is still much to learn about it. Scientists agree that starry stonewort thrives in lakes of Southeast Michigan; low-nutrient, transparent lakes with calcium carbonate-rich sediments. 

As the tour goes upstream into Kent Lake, we meet another exotic invasive—curly-leaf pondweed.  This plant is generally not as widespread as starry stonewort or Eurasian watermilfoil, but it can cause problems at some locations. Curly-leaf pondweed differs from the many native pondweeds, sporting leaves that look like Ruffles potato chips. 

The tour continues upstream, repeating the same plants ad nauseam; starry stonewort and invasive watermilfoil primarily in the natural lakes and impoundments; and phragmites, flowering rush, and purple loosestrife along the banks. To cap off the tour, we reach Pontiac Lake, very close to the Huron headwaters at Big Lake. Except for frogbit and water clover, Pontiac Lake has the misfortune of holding every invasive aquatic plant mentioned thus far in this report.  

Vigilance for a wide-spread problem 

Starry Stonewort. credit: Scott Brown

All these plants are also found on the hundreds of lakes not directly connected to the river. The MISIN data identifies 34 Huron River watershed lakes plagued by starry stonewort, ten afflicted with Eurasian water milfoil, and eight infested with curly-leaf pondweed. These numbers are likely much higher because not every lake is monitored and/or reported.   

Unfortunately, once plants establish themselves in the ecosystem, permanent eradication is nearly impossible. The phragmites, flowering rush, and purple loosestrife that make up a large portion of the Huron River’s riparian zone are here to stay. It is possible yet very expensive to treat specific stands of the plants that are particularly troublesome or invade habitats that are particularly important.   

As sad as this analogy is, suppressing invasive species is not much different than suppressing a virus. It takes vigilant isolation and decontamination policies. If any of these exotics spread to a new water body, it is important to stop the plants immediately before they become established. As the watershed’s lakes seem particularly susceptible to starry stonewort invasion, a pristine lake that is surrounded by other lakes infected with starry stonewort requires relentless monitoring to extinguish any accidental introduction of this plant.  

For lake ecosystems with boat launches, the battle takes place at those locations. Lake associations need to station people at boat launches on busy weekends to check that boats are not bringing in unwanted plants. Monitoring at boat launches is not easy and requires a vigilant, concerted effort. Any boat—including simple canoes and kayaks—can bring in plants, though it is easiest for plants to hide on boat trailers. Two important programs for lake residents to be aware of are the Exotic Plant Watch program through the Michigan Clean Water Corps, which trains people to look for aquatic invasive species, and the Clean Boat Clean Waters program, which offers training and materials to volunteers who want to monitor their boat launches.  

For stream ecosystems, it is even harder to prevent contamination since there is no primary place where something can be introduced. Education is the key—all river users must become aware that they can easily spread invasive species from one place to another. HRWC uses bleach and/or Formula 409 to decontaminate all monitoring gear and waders when moved from one place to another—and encourages anglers and boaters to do the same. Paddlers on our river and stream ecosystems can get involved with Michigan Paddle Stewards, which helps paddlers identify and map invasive species along Michigan’s water trails. 

This is not the plants’ fault

As a final point, I would like to address the fact that plants are clearly unthinking things that have no motivations to alter and ruin our ecosystems.  Humans brought the plants here, after first creating such a welcoming and verdant environment for them!  There are impounded lakes where there should be a free flowing river, and our aquatic systems are laden with phosphorus thanks to human activity on the broader landscape. The fault lies not with the plants themselves, but rather human hubris as well as ignorance

Let us try to stop these plants from spreading, but it is also the human responsibility to prevent the types of changes to the landscape that make it so easy for the plants to grow in the first place! Constant vigilance!

Other resources:  

Summer 2016 Huron River Report cover article “Aquatic Hitchhikers”

Mi-Corp  Invasive Species Prevention kit, video and users guide

Exotic Plant Watch program through the Michigan Clean Water Corps

Clean Boat Clean Waters program including training and support materials 

Waterfront Wisdom

Michigan Paddle Stewards

This blog post was originally published June 1st in the Huron River Report, Summer 2020.