Eurasian Watermilfoil Found Growing in Little Glen Lake

by | Sep 19, 2024 | Invasive Species, News

Back in September 2023, Glen Lake Association (GLA) Boat Wash Manager Victoria Velting found a few strands of Eurasian watermilfoil (EWM) floating in the lake near the Day Forest Road boat launch. The discovery prompted the GLA to establish an EWM Task Force to respond to the threat and investigate the source of the strands.

Since then, the GLA has not stopped looking for EWM. Over the course of the past year, we have partnered with two companies and employed multiple methodologies to survey Little Glen and a small area of Big Glen east of the Narrows. Using drone technology, contractor Zero Gravity captured nine hours of high-resolution video of the lake bottomlands, traversing 24 miles in a grid-like flight path. GLA Watershed Scientist Rob Karner subsequently studied the footage, identifying 38 high-risk areas which were later investigated on-site using underwater cameras. In parallel, contractor Restorative Lake Sciences (RLS) performed a scan of more than 47,000 GPS points using georeferencing technology. RLS then surveyed over 1,000 of those locations using a rake toss sampling technique. Neither Zero Gravity nor RLS found any evidence of EWM. However, EWM in its early stages is difficult to find.

Then two weeks ago, almost one year to the date of her original discovery, Victoria spotted more strands of EWM floating near the boat ramp. Noting strong, southwesterly winds that day, Rob Karner worked with GLA Assistant Scientist Joe Blondia and Zero Gravity’s Dennis Wiand to map out and execute a search strategy. Within days, the team located an established EWM colony growing at 13 feet deep. The colony they found spans approximately 35 feet at its widest point and covers approximately 1,200 square feet in total. While this area represents a small fraction of Little Glen’s overall surface area (1,400 square acres), it is a big problem.

If left unchecked, EWM can significantly alter a lake’s ecology. The aggressive nature of the plant enables it to reproduce from small fragments and rapidly spread. As plant fragments break off either naturally or from boating and fishing activity, they float to other areas of a lake where they can establish new colonies. As EWM colonies grow, they form large dense mats of floating vegetation which interfere with recreational activities such as boating, fishing, and swimming. In addition, EWM “shades-out” native aquatic plants by restricting the passage of light and can negatively impact fish and waterfowl populations.

The GLA’s Boat Wash operates from early May through late October each year in a valiant attempt to prevent aquatic invasive species like EWM from entering Glen Lake. Each season, Boat Wash staff visually inspect more than 4,000 watercraft, wash more than 900 watercraft with high-pressure hot water, and flush more than 600 motors. However, EWM can be introduced into the lake in ways the Boat Wash cannot prevent. For example, the plant can live for weeks inside the jet intakes of personal watercraft or inside boat engines. It can also be transported from lake to lake by waterfowl. Nearby lakes including Crystal Lake, Lake Leelanau, and Houghton Lake, have been fighting EWM infestations for years. In doing so, their communities have invested significant time and money and have learned a lot about what works and what does not work well. We hope to benefit from these lessons learned.

The GLA is actively working to formulate a treatment plan for the identified EWM colony in Little Glen. There are a number of treatment options, all of which will be thoroughly considered by the Task Force. We will also continue to explore other areas where EWM could be present. At this time, we do not know if there are additional colonies established in Little Glen, or if there are any colonies located in Big Glen. EWM was also recently found in the upper reaches of the Crystal River, and the GLA is working with the National Park Service to eradicate it there. Going forward, the lakes and rivers will require constant surveillance and, likely, regular treatment to keep EWM at bay.

Please forward this email to anyone you know who is not already a member of the GLA. More than ever, we need to raise awareness and resources to fight this battle and “Keep It Blue!”

Photo by Rob Karner