As our field season wraps up for the year, we wanted to share our progress in controlling Eurasian watermilfoil using non-chemical methods in Lake Leelanau. We invite you to read our blog post to learn about what our crew has accomplished this year.
Five Years of Work
For the 5th year, the Lake Leelanau Lake Association (LLLA) and the Grand Traverse Band of Ottawa and Chippewa Indians (GTB) partnered to protect Lake Leelanau from the invasive Eurasian watermilfoil. Eurasian watermilfoil, or EWM, has been described as one of the most invasive and noxious aquatic invasive species in North America due to its ability to grow up to the surface of the lake in thick, dense mats which inhibit recreational and ecosystem functions of the lake. EWM can reproduce from a fragment less than a couple of inches long, making it an expert colonizer and a huge danger to Lake Leelanau.
LLLA and GTB have dedicated the past 5 years to controlling the spread of EWM using non-chemical methods. 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. These barriers, made of biodegradable burlap blankets, are laid on top of the plant which inhibits its ability to photosynthesize and kills it.
Lessons Learned
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. 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.
This new strategy has come with some new lingo. Once an EWM colony is covered using the “no strand left behind” rule, it becomes a “maintenance site”. The crew will continue to go to that site and rid it of any EWM that was missed or that floated from a nearby colony and landed on the burlap, sending roots down through it from above. As more and more of the large infestations in Lake Leelanau are converted into “maintenance sites” and the number of fragments floating through the lake are reduced, there is a possibility that no EWM would return to these sites, “locally eradicating” it. The crew will only consider a site to be “eradicated” if no EWM has been detected there for three years in a row.
New Innovations, Less EWM
The crew is constantly learning and adjusting their methods as they spend more time working to control EWM in Lake Leelanau. Burlap is now used to kill everything from individual EWM strands covered with a single burlap bag filled with pea gravel, to large infestations using a hybrid boat-diver approach to set hundreds of feet of burlap at a time, as seen in the photo above. This method has eliminated the need to employ a small army of volunteers to deploy great lengths of burlap like in year’s past and has immensely increased efficiency.
The crew’s efficiency in covering the EWM was also drastically improved this year due to hiring twice the staff they had last year, fielding six seasonal SCUBA divers and two field technicians. The seasonal staff joined LLLA lake biologist, Ron Reimink, and Director of Administration and Programs and Dive Team Leader, Annalise Povolo, in addition to numerous GTB staff and volunteer extraordinaire, Lonnie Rademacher.
With the adoption of the “no strand left behind” rule in 2023, the crew started the season by returning to the previous year’s sites and ensuring they were free of EWM. The increased care paid in 2023 to cover every identifiable strand proved successful, it only took a little over a week to get all five maintenance sites from 2023 back to the point where no EWM was discovered in the area. The crew then moved on to other sites where burlap had previously been set before the new rule was adopted, which required some additional effort, but were ultimately added to the ¨maintenance sites¨ list. The larger crew finished covering the last remaining large infestations of EWM this year and there are now 14 areas in South Lake Leelanau that have moved into the “maintenance site” phase and are clean of EWM. This includes the massive Gordon’s Point site (the largest yellow point on the map), where around 3.5 acres of burlap was set last year, which is now EWM-free. The crew will continue to return to these sites year after year to ensure they stay that way.
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 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.
It Takes a Village
The accomplishments of this field season would not have been possible without the helping hands of many. As always, LLLA is incredibly grateful to the Grand Traverse Band of Ottawa and Chippewa Indians for their partnership 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. And last but certainly not least, the volunteers! From board members, committee members, to community members, LLLA volunteers have put in over 400 volunteer hours this year helping with boat washing to prevent the spread of aquatic invasive species, performing invasive species early detection surveys, and they have filled over 3,000 bags of pea gravel to weigh down our burlap barriers. What an incredible showing of community support.
We want to especially express our gratitude to Darlene Doorlag, for the priceless donation of her lakefront property and storage spaces for the crew to operate from and store their boats and materials. The program would not have measured the same level of success without access to this space. Thank you, Dar!