Lake Archer, Wrentham, MA June 25, 2026 hand-harvest dive day
On our June 25, 2026 dive day, our hand-harvesting divers pulled just one bag of invasive Eurasian watermilfoil from Lake Archer. Most of the lake was largely clear. About half of the little we did harvest came from new patches we located with sonar surveying before the divers ever got in the water. After four years of active management, the lesson is simple: once you get ahead of milfoil, winning is about finding it fast and diving small and often to stay ahead of it.
Just one bag of milfoil harvested on the June 25 dive day.
Most surveyed areas were largely clear of invasive growth.
New patches, found by sonar surveying, made up roughly half of what we harvested - proof that locating milfoil early is where the value is.
Results reinforce our "garden" philosophy: frequent, smaller dives keep milfoil small, before it can fragment and spread.
Once you have contained a big infestation, the hardest - and most expensive - part of manual milfoil control is no longer pulling plants. It is finding them. Paying skilled divers to swim the lake hunting for scattered plants is costly and slow. So we put our effort into pinpointing milfoil precisely first, then sending divers straight to it. Smaller, more frequent dives let us harvest plants while they are still small - the single biggest factor in staying ahead of Eurasian watermilfoil year after year.
This season we added an inexpensive trick that made diving dramatically more efficient:
Locate the patches with sonar. Our sonar surveying, analyzed with a machine-learning algorithm on the sonar recordings, pinpoints exactly where milfoil is growing.
Drop an auto-depth marker buoy on each patch. We use small, inexpensive marker buoys (the Ozark Trail 2-pack marker buoy). We remove the weight from the center wrapper so the buoy self-adjusts to the water depth, then toss one onto each patch the sonar located.
Divers work between the orange buoys, searching within about 20 feet of each buoy for plants to harvest.
The payoff: divers go straight to the plants that need harvesting instead of spending hours searching, so far more milfoil is removed per dive hour at a fraction of the search cost.
Hand-harvesting dive team: At The Water's Edge
DASH (Diver-Assisted Suction Harvesting) for milfoil and Brazilian waterweed: New England Aquatic
Sonar surveying to locate milfoil: Milfoil Finder
If your lake is fighting Eurasian watermilfoil, here is Lake Archer's takeaway after four years: you can contain milfoil without whole-lake herbicide treatments by (1) locating it precisely with sonar surveying, (2) marking each patch with cheap auto-depth buoys, and (3) diving small and often to harvest plants while they are still small. We are glad to share what we have learned - reach us at board@lakearcher.net.
At the Lake Archer Association (LAA), we believe in sharing the results of our hands-on efforts to manage invasive species. Through thfourree years of active management, we have found that a methodical, manual approach allows us to contain milfoil while protecting the lake’s vital natural biodiversity.
Through field observations and data collection, we have developed a strategy based on several key experiences:
The "Garden" Philosophy: We have found that milfoil management is more like weeding a garden than shaving a beard. If you stay ahead of it with frequent visits (every 4–6 weeks), the work of keeping it contained is significantly smaller than the work of taming a full-scale infestation.
The Power of Manual Harvesting: We have found that a combination of hand-harvesting divers and DASH (Diver Assisted Suction Harvesting) is highly effective. Other lakes have seen similar success; for example, the 1,000-acre Otis Reservoir reduced milfoil from 50 buckets to just 1 bucket in three years using these manual methods [1].
Solving the Search Bottleneck: We have found that the biggest expense in management is "search time." By using our MilfoilMapper sonar technology to identify weed beds before divers enter the water, we ensure that their time is spent pulling weeds rather than searching for them.
While chemical treatments like ProcellaCOR are a common consideration, our review of the data and local conditions led us to prioritize manual removal. We have found several compelling reasons for this choice:
Cost Realities: While a manual dive program is a significant investment—costing approximately $20,000 annually (based on $7,500 for 5 days of hand-harvesting and $13,749 for 5 days of DASH)—we found it to be more efficient than herbicides for our current state. An herbicide treatment for 17 acres would cost between **$32k–$38k**, and because ProcellaCOR is milfoil-specific, it would not address other invasives like Brazilian Waterweed, still requiring manual diving afterward.
Protection of Native "Good" Weeds: We have found that native plants like Coontail are essential to Lake Archer, making up nearly 40% of our ecosystem [2]. Research indicates ProcellaCOR can cause a 60–70% reduction in Coontail in treated areas, and up to a 30% reduction in untreated areas [3]. This removes the natural competition that prevents harmful algal blooms.
Health and Environmental Observations: Our research highlighted studies showing potential impacts on freshwater wildlife, including neurological development issues in fish [4] and harmful negative impacts on invertebrates, insects, and trout at all treatment levels [5]. Furthermore, we noted evidence of harmful mouse and rat side effects in laboratory settings [6].
Preserving Tool Efficacy: We have found evidence that milfoil can develop resistance to ProcellaCOR [7]. We prefer to maintain a manual program and save chemical options as a last resort to prevent the development of resistant "super-weeds."
We don’t profess that this is the only way to manage a lake, but we have found it to be the most responsible and effective path for Lake Archer. We are working on a way to share access to the MilfoilMapper software and our "Scout & Mark" workflow so that other associations can see how we turned technology into a tool for environmental stewardship.
The information shared on this site is an account of the findings and results experienced by the Lake Archer Association. These results are specific to our weed density, water chemistry, and volunteer efforts. We recommend all lake associations consult with aquatic experts and local regulatory bodies.
[1] Otis Reservoir Management Success: From 2021 to 2023, Otis Reservoir (1,000+ acres) went from 50 five-gallon buckets to 6, and finally to just 1 bucket using DCR-recommended hand-harvesting.
[2] Native Vegetation Density: Native "good" weeds make up 21% to 40% of Lake Archer's ecosystem.
[3] Impact on Coontail: VT 11 Lake Post-Treatment Survey showing significant reduction in native plants following herbicide use.
[4] Fish Neurological Impact: Toxicity Study on Freshwater Fish (Video) showing developmental impacts.
[5] Impact on Non-Target Species: Beyond Pesticides Report (2025) regarding threats to biodiversity and aquatic species.
[6] Mammalian Lab Studies: Evidence of mouse/rat side effects including mammary gland tumors and organ weight reduction (Reference #42-45 in LAA Draft).
[7] Herbicide Resistance: Documented evidence that Milfoil develops resistance to ProcellaCOR (Reference #58 in LAA Draft).
[8] Lake George Persistence Case Study: Environmental Persistence Video showing chemical tracers persisting longer than initial assumptions.