Aquatic invasives threaten area waters

Photo: Members of the Lake Leelanau Lake Association hose down a boat.

By Ross Boissoneau

Sun contributor

For many people visiting and moving here, it’s all about the water. Unfortunately, the same is true for other, less-welcome entities: Eurasian watermilfoil (EWM), Quagga mussels, purple loosestrife and other invasive species.

Combating these and other unwelcome plants and animals is an ongoing challenge. For example, Lake Leelanau has been in the news for its battle against Eurasian watermilfoil, a plant native to Europe, Asia, and North Africa. Now Glen Lake has discovered signs of the plant. If unchecked, it spreads quickly and forms thick mats in shallow areas. It blocks sunlight and kills native aquatic plants that fish and other underwater species rely on for food and shelter.

Glen Lake Association watershed biologist Rob Karner says treating invasives follows a simple formula: find it, deal with it, and repeat until it’s gone. But while the formula may be simple, it’s far from easy.

For example, while Eurasian watermilfoil can be treated with an herbicide, that can impact other plant life. Removing it manually is possible, but any fragment that escapes can re-root and start the lifecycle again, making it a huge challenge.

Lake Leelanau has battled it since it was first discovered in 2019. The Lake Leelanau Lake Association (LLLA) has tried carefully harvesting the plant, but has now begun treating infestations by laying a covering of biodegradable burlap on the lakebed where the weed is growing. That kills both EWM and other plant life, but native plants have been seen regrowing as they have established seed beds. “In two years, the burlap has degraded and we’re just left with some pea gravel on the corners,” says LLLA President Nancy Popa, referencing the bags of gravel used to weigh down the burlap. “So far, the native plants are returning.”

Now Glen Lake is undergoing surveys to determine exactly where and how bad its infestation is. “We’re employing as much technology as we can,” says Karner. That can include everything from airborne and underwater drones to Google Earth and geolocating the sites.

It’s not just plants. Kyla Robinson is the aquatic invasive species coordinator for the Benzie Conservation District, which covers Leelanau, Grand Traverse, Benzie and Manistee Counties. She says one of the biggest challenges for rivers is a nearly microscopic animal. “For rivers, a big one is New Zealand mud snails. They’re the size of a tiny grain of rice. They’re really prolific and reproduce asexually. They can take off and create dense populations.” She says they are spreading throughout northern Michigan, and have been found in the Boardman River, Mitchell Creek and Cedar River near Bellaire.

Another Robinson is on the lookout for is didymo, also known as rock snot. The coarse, wooly alga can grow into thick mats that cover the river bottom.

Robinson says studies have shown most invasives are spread by people, typically through boats being moved from one waterway to another. “Our region is famous for tourism,” she says, and many of those visiting bring or rent a boat. “The common pathway is the boat goes in, then out. Within a week they may be in three or four waterways.”

That’s why it is vitally important to clean the watercraft before relaunching them. Many of the popular lakes see that need and have installed boat washes. But that’s expensive and is easier some places than others.

For example, Glen Lake has one public access, at which it has installed a boat wash. That’s not so easy at Lake Leelanau. “We have 14 public access points,” says Popa. The association has installed public boat washes at the four largest launch points and is trying to direct boaters there. At a cost of approximately $35,000 each, trying to place one at each of its accesses is a non-starter.

While Eurasian watermilfoil has gotten the most attention publicly, but it’s far from the only problem. Though the Northwest Michigan Invasive Species Network concentrates on terrestrial invasives, among its Top 12 invaders (think the dirty dozen) are purple loosestrife and invasive phragmites. Both are concerns of lake groups as they grow in wetlands and can clog waterways as they collect silt. They crowd out native flora and are unfriendly to native plants and animals, such as waterfowl.

Karner says another shoreline invader the Glen Lake association has been doing battle with is yellow flag iris. It forms dense mats of rhizomes and crowds out native plant species. Karner says Glen Lake has seen a dramatic reduction in infestation, with 40 to 50 documented locations down to just a few in the three years since it was identified as a threat.

He also points to a population of Japanese Koi as another problem. Karner says the fish were identified in the lake five years ago, and they will outcompete native fish for food and habitat. He says the plan is to locate them and catch and kill them with bowfishing.

Though they face greater challenges due to their popularity, larger lakes like Glen Lake and Lake Leelanau also boast greater resources to identify and combat invasive species. Robinson says there are a number of smaller lakes in the county that do not have active lake associations, which makes them more vulnerable.