As summer winds down, so has our time spent on Lake Leelanau controlling Eurasian watermilfoil (EWM) for the year. This summer marked the 6th year of control efforts, bringing with it more lessons, innovations, and areas cleared of this pesky invasive species. Learn about the status of our work in this year’s EWM Update.
All Eyes on the Lake
Surveillance is a primary mission at the beginning of the season. Our crew eagerly awaited the day when the dock and boats were put in so they could get out on the lake to check up on our Eurasian watermilfoil (EWM) treatment sites from years past and see how they held up over the winter. This year’s initial survey alluded to positive results, though the early-season monitoring must be taken with a grain of salt, as the plants “wake up” from their winter nap at different times each year.
Once mid-June rolled around, our seasonally contracted divers joined us again, and our top priority was to get out and do diver surveys of the “Maintenance Sites” (see last year’s EWM Update for an explanation of Maintenance Sites). Those sites were completely clean of EWM at the end of 2024, and it is our objective to keep them that way. This year, we were more thorough than ever to ensure that we hadn't missed a strand of EWM the year before, and that any fragments from elsewhere hadn't settled and re-infested the burlap. Each site was surveyed by divers twice at the beginning of the season. Very little EWM was discovered, most of which was only growing sparsely outside the edges of the burlap or where there was an anchor strike on it.
Several sites had no observed EWM growing on or off the barriers. One such site is the south side of the Narrows. This is a crucial site for us to keep free of EWM due to its proximity to North Lake Leelanau, which still does not have any EWM infestations. This site was very well taken care of in previous years, and has now had no EWM observed for a whole year, and a healthy and diverse population of native plants in its place.
The main lesson learned after diving on barriers from years past was “Go Big or Go Home”! Any EWM observed on the former Maintenance Sites was thought to be there as a result of roots creeping out from under the barrier, meaning it really needed a larger piece of burlap to properly cover it. The crew took this lesson to heart, and in 2025, covered even single strands of EWM with larger pieces of burlap than before to ensure no roots or strands were close enough to the edge to grow.
Native Regrowth
Native aquatic plants (native milfoil, pondweeds, and water celery, amongst others) growing where there was previously EWM and then burlap set in 2021. Native plants have been seen growing on burlap set on EWM within one month, showing a natural recovery of native plants in areas previously infested with EWM.
A New Approach and a New Discovery
After thoroughly surveying and covering any remaining EWM on the Maintenance Sites, our crew started expanding to survey the surrounding areas, moving towards an approach of covering “regions” instead of just “Maintenance Sites”. This is important as small fragments can break off from larger EWM strands and propagate nearby. After thoroughly inspecting the barriers at those Maintenance Sites, our crew extended beyond the barrier to survey the overall region at the depth profile at which EWM can grow.
As our crew surveyed larger regions, a new resurgence of an infestation was discovered. It had not previously been noted because it was in deeper water and very mixed in with native aquatic plants. This region had a significant amount of EWM. We set 1.33 acres of burlap to cover the EWM there. This accounted for 57% of the burlap set over the entire season, 2.32 acres. For comparison, 2.87 acres of burlap were set in 2024, and 5.22 acres were set in 2023. We are cautiously optimistic that, even though we placed more burlap than before to cover the same-sized infestation, we will see these numbers continue to decrease.
A New View: The Underwater Gardens of Lake Leelanau
Other than the one larger infestation, diving in Lake Leelanau this year was a different scene than in years past. Where previously we were diving exclusively over monoculture infestations of Eurasian watermilfoil, the majority of the summer was spent glorying in the beautiful native aquatic gardens, searching for individual strands or clumps of EWM.
Our methods have improved, and we have covered a lot of EWM that, as long as we cover it completely, has not come back. We are hopeful that more and more sites will be EWM-free next year, but still, we never know what nature will bring.
Our Sincere Gratitude
None of this success would be possible without our incredible team of staff, volunteers, and partners. As always, LLLA is incredibly grateful to the Grand Traverse Band of Ottawa and Chippewa Indians for their partnership and contributions in this work.
Huge thanks go out to all of the LLLA staff members who put their blood, sweat, and tears into protecting the lake (read more about our crew here). We had an incredible crew this year who made this often difficult work still fun. Thanks, field team!
We want to especially express our gratitude to Darlene Doorlag for the priceless donation of her lakefront property and storage spaces from which the crew stores their boats and materials. We would also like to thank Mark Woolsey and John Heekin and his crew for their immense efforts in helping us care for the property while we were busy on the lake. Thank you!
And last but certainly not least, the volunteers! From board members, committee members, to community members, LLLA volunteers have put in hundreds of hours this year helping with boat washing to prevent the spread of aquatic invasive species, walking their shoreline to look out for EWM washing up on North Lake Leelanau, and filling over 2,000 bags of pea gravel to weigh down our burlap barriers. What an incredible showing of community support. It truly does take a village, and we are so lucky to have such an incredible community behind us.
If you would like to read more about our efforts to control Eurasian watermilfoil with biodegradable benthic barriers on Lake Leelanau, please read our Field Reports on our website, and stay tuned for the 2025 Field Report later this fall.
