Things are looking up for Lake Leelanau’s battle against an extremely destructive invasive plant. Five years after Eurasian watermilfoil (EWM) was first detected in Lake Leelanau, the Lake Leelanau Lake Association (LLLA) says it has established an efficient and reliable strategy for stamping out infestations.

In a blog post published this week, the LLLA detailed its summer 2024 fight against EWM, describing the past several months as “a very successful field season.”

For the past five years, LLLA has been teaming up with the Grand Traverse Band of Ottawa and Chippewa Indians (GTB) to combat EWM spread. When left untreated, EWM can create thick mats of growth throughout a lake, blocking sunlight, killing off native plant and fish species, and causing problems for watercraft, among other problems. In their collaborations, LLLA and GTB have been testing a variety of “non-chemical methods” for combatting the plant.

“After trying and testing several non-chemical control methods to determine the best option, the partners now solely rely on benthic barriers to kill EWM,” LLLA shared in its blog post. “These barriers, made of biodegradable burlap blankets, are laid on top of the plant which inhibits its ability to photosynthesize and kills it.”

While LLLA and GTB have been using benthic barriers to fight EWM for several years, LLLA says those efforts have become more productive recently, thanks to the adoption of a “no strand left behind” rule last summer.

“One of the most important and hardest lessons the crew has learned over the years is that every single strand of EWM must be covered for the burlap barriers to function, otherwise any EWM left on the edges can recolonize the barrier,” LLLA wrote. “This lesson has inspired a new approach in which the crew does not leave an infestation until they are at least 95% sure that all of the visible infestation has been covered with burlap. Since this method’s adoption in 2023, the crew has found that very little maintenance is required if the ‘no strand left behind’ rule is followed.”

Per LLLA, EWM colonies covered with burlap in accordance with the “no strand left behind” rule then become maintenance sites, which SCUBA crews monitor for new growth but haven’t had to spend as much time treating. Additionally, the new strategy has meant fewer EWM fragments floating through the lake and establishing new colonies. Burlap-covered EWM sites that haven’t seen any new growth in three years are considered “locally eradicated.”

So far, the new approach is yielding results. LLLA says that all five maintenance sites from 2023 are now to the point “where no EWM was discovered in the area” this year. Additionally, Gordon’s Point, a site in South Lake Leelanau where LLLA and GTB laid down a whopping 3.5 acres of burlap last summer, had no EWM growth this summer, becoming one of 14 new maintenance sites in the lake.

“By the end of the season, the crew was able to move on to the small infestations that had previously been low on the priority list while they had been preoccupied tackling the larger, more easily spreadable, infestations,” the LLLA blog post continued. “crew spent their dive days of the season swimming for hours in the water, only to find a few sprigs of EWM to cover each day. Who knows what next year will bring, but for now, the EWM crew is proud to put their feet (or fins) up and toast to a very successful field season.”