Lake Iroquois milfoil cleanup planned

Milfoil, an invasive aquatic plant, has taken over much of Lake Iroquois. Photo by Pogo Senior

Eurasian milfoil created a smelly mess for visitors and homeowners last summer at Lake Iroquois. This year, the Lake Iroquois Association has a plan to deal with the invasive aquatic plant, which has already taken over a significant portion of the lake.

The Lake Iroquois Association has formulated a five-year milfoil removal plan, including treatment of the lake with the herbicide Sonar this year, said LIA Director Jamie Carroll. The herbicide treatment comes with a price tag of $100,000, $30,000 of which will be provided by the town of Hinesburg following a Town Meeting vote. The remaining funds will come from Williston, and from private donors.

A permit is expected soon. The LIA will hire a contractor who will apply the herbicide from a boat in the areas where milfoil currently grows. The first application is planned for May, with subsequent treatments to follow as needed, possibly in June, July, and August. The targeted concentration of Sonar in the lake will be eight to 10 parts per billion; a Vermont Department of Health document notes that the active ingredient in Sonar must not exceed 20 ppb.

The lake will be closed to visitors for a few days following each application. Carroll noted that samples will be taken 24 hours following application, and these must be shipped to a lab, adding time to the lake’s closure. Once Sonar levels are deemed to be safe, use of the lake may resume; the goal is to perform each treatment on a Monday or Tuesday so that the lake may reopen by the following weekend.

The herbicide will affect not only the lake’s recreational users but also the homes surrounding the lake. The DOH document notes that domestic water use should be restricted in 24-hour increments until both Sonar’s active ingredient and another chemical are found to be below acceptable limits in the lake and its outlet waters. Carroll said that while no public drinking water is drawn from the lake, some nearby homes and camps do draw water from Lake Iroquois for various household uses, including filtering and drinking, bathing, and flushing. LIA will offer bottled water to these users during periods of treatment, Carroll said.

Sonar breaks down in sunlight, said Department of Environmental Conservation Environmental Analyst Misha Cetner, but the timing of this depends on several factors including temperature and amount of sun exposure. The herbicide is applied in low doses over a longer term, meaning it does not break down immediately in the water. Some of the herbicide, therefore, will likely reach Sunset Lake and potentially Lewis Creek, said Carroll.

The herbicide to be used, Sonar, is fairly targeted to Eurasian milfoil, noted Cetner. There are two general types of aquatic plants in the lake, noted Carroll: broad-leaf and narrow-leaf. Milfoil is the former, but most aquatic plants in Lake Iroquois are the latter, lessening the impact that Sonar will have on non-target plant species, Carroll explained.

Before and following each treatment, Carroll said, testing and monitoring will take place to assess the herbicide’s impact in the lake, with a more comprehensive survey to take place next fall. From there, the five-year plan includes non-herbicide milfoil control efforts, including benthic mats (placed on the lake floor to prevent milfoil growth) and potentially a return of the suction boat that was brought in last summer.

The impacts of milfoil on Lake Iroquois are multiple, said Carroll. In 1984, 45 aquatic plant species were found in the lake. Ten of those had disappeared from the lake by 2012, and even fewer species were found in a 2014 survey.

“In a lot of places milfoil’s really becoming a monoculture,” said Carroll. Such conditions create a poor habitat for fish species in the lake.

And “the lake is an important resource for recreation in the area,” said Carroll, but this is curtailed when large portions of the lake have been overtaken by milfoil. The lake’s total area is 244 acres; 105 of those are littoral zone, which can support aquatic plants. Of these 105 acres, 70.7 acres, or over 60%, are already infested, with an additional 33 acres awaiting milfoil’s takeover. The problems don’t just stop at Lake Iroquois, either: the invasive plant can spread via boats to other waterways.

Milfoil’s impact is also economic. Over 22 million dollars’ worth of properties lie on the lake’s shore; Hinesburg receives $450,000 annually in property taxes from Lake Iroquois properties. Milfoil removal “improves the recreational value” of these properties, said Carroll, with such activities as boating, paddling, and swimming all playing a role.

Other similar properties have provided a glimpse at what can happen to lakefront properties when environmental issues are not addressed, Carroll added. Lake Champlain lakefront properties where algae blooms have occurred have seen decreases in their property values, and studies from N.H. have shown a similar pattern in lakefront homes affected by milfoil.

Public support has been a major part of getting the milfoil mitigation project launched, said Carroll. “The Lake Iroquois Association and all the users of the lake are grateful to the towns for their support in being able to make these treatments happen.”

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