Updated June 2020
Where are we now and where are we going?

The goal of our previous Save Stockbridge Bowl plan, as approved by the relevant Massachusetts agencies, was to pursue a 5.5 foot winter drawdown of the lake. The drawdown would have frozen and killed the invasive Eurasian milfoil growing out to a depth of 5.5 feet. (Beyond that depth, the milfoil could continue to grow unimpeded to a water depth of 16 feet.) The drawdown was accompanied by a dredging plan to increase the waterflow in the Outlet in the southwestern part of the lake towards the dam.

In 2018, those efforts were stymied by the Massachusetts Natural Heritage Endangered Species Program (NHESP), which is responsible for protecting marginal species of plants and animals. NHESP reversed its earlier approval of both a 5.5 foot drawdown and our proposed dredging plan. Instead, NHESP recommended that Stockbridge use an herbicide, specifically fluridone, to control milfoil. The NHESP informed the SBA that it had concluded, based on an updated study, that a 5.5 foot drawdown would threaten the habitat of the rare and endangered M. Lustrica snail.

Given NHESP’s position, the SBA shifted its strategy for the lake plan to include three simultaneous efforts:

  1. Application of the NHESP-recommended herbicide, fluridone, to treat and rid the entire lake of the invasive milfoil;
  2. Modified dredging behind Kwuniikwat Island and in the Outlet to prevent those areas from becoming a bog; and
  3. Selective hydro raking to manage the density of water lilies in the southwestern part of the lake.

This approach will facilitate the restoration of the lake, benefit the largest population of constituents, and allow the outlet to have adequate water flow. These steps each require different permitting processes with the Town and the State, as required by Massachusetts regulations, in addition to also having different costs and timelines. The SBA, in coordination with the Town of Stockbridge, collaborates on each step of this restoration plan.

Next Steps and Timelines

Herbicides -​ The SBA is proceeding with the Mass. DEP (Department of Environmental Protection) to set up a 3-part test of fluridone on the lake with a follow-up study, anticipating larger application in 3-4 years, pending the outcome of DEP’s testing protocol. ​The goal ultimately is to use fluridone to control milfoil throughout The Bowl. In late summer 2020, the SBA will comply with a DEP requirement to count the stems of all vegetation in two large test plots – one along the south shoreline and the other along the west shore just above Kwuniikwat Island. In spring 2021, the test plots will be treated with fluridone. In 2022, the stems of native plants will be counted to confirm their regrowth in the test plots. Assuming no adverse impact to the native plants, we will be able to proceed with a 2023 application of fluridone to the entire lake.

Dredging​ – ​To prevent the areas behind Kwuniikwat Island and down the outlet from becoming a bog, a channel needs to be dug through those areas, which requires permission from NHESP. In order to proceed, we will need to get additional financial support from the Town and from the Bowl community. ​The Town, GZA, the contractor with which the Town is working, and the SBA are currently in agreement regarding the dredging plan behind Kwuniikwat Island and down the Outlet. As of Monday, March 23, 2020, the SBA, the Town of Stockbridge project manager and GZA are waiting for the Net Benefit proposal. In this Net Benefit Plan there must be an impact statement regarding the snails (Marstonia Lustrica) and how we plan to offset the impact of any work and keep the habitats alive. No matter what we do at the end, there will be costs beyond the dredging portion. ​ ​ In order to proceed, we shall need to get additional financial support from the Town and from the Bowl community.

Hydro Raking– TBD ​based on conversations with DEP. Based on the lilies’ growing cycle, hydro raking would commence at some point in the future. Hydro raking has two parts that may include a privately funding homeowner portion to reduce density surrounding docks in addition to the lake maintenance. ​We’ll evaluate the effectiveness of the hydro raking employed in late 2019 in front of one home and seek ConComm (Conservation Commission) approval to hydro rake other shoreline properties. The SBA will fund putting the hydro raking equipment in and taking it out of the lake. Individual homeowners will fund the balance.

The Town is working on a Notice of Intent (NOI) for weed harvesting and recently submitted the paperwork. We are optimistic that we will have an operational harvester during the 2020 summer season.

Permitting, Planning, Funding and fundraising for all of these projects are currently part of the core mission of the SBA

Frequently Asked Questions

What Herbicide? ​The selected herbicide treatment for milfoil is fluridone (sold under many different brand names – Sonar, Avast, Whitecap). Submersed Aquatic Vegetative Studies, commissioned by the SBA from Solitude, have been completed, giving us a complete picture of the weeds in the lake. The first priority is to treat the milfoil, which is the most abundant weed. The study showed three other invasives in the lake, but in significantly smaller amounts.

What is Fluridone/Sonar? ​Fluridone is an organic compound known as an aquatic herbicide. It was registered with the EPA in 1986. See below for more information on its chemical composition.

Where is it currently used? ​Herbicides, including fluridone, have been safely used for decades in more than 300 Massachusetts lakes and ponds to control milfoil. (This includes Lakes Onota and Pontoosuc in Pittsfield, Richmond Pond, Goose Pond in Lee and Otis Reservoir) plus thousands of lakes in other states.

How does it work? ​Fluridone breaks down the plant’s photosynthesis process. Specifically, fluridone inhibits the formation of carotene, a plant pigment, causing the rapid degradation of chlorophyll by sunlight, preventing the formation of carbohydrates necessary to sustain the plant. It is absorbed from the water by the plant’s shoots and from the hydrosoil during the growth phase of the plant. A slow dying-off of plants (i.e. 30-90 days) reduces the instantaneous oxygen demand that would have been caused by plants dying and decomposing all at once. The herbicidal effects of fluridone usually begin to appear within 7-10 days.

How do the active ingredients break down? ​The time it takes for half of the active ingredients to break down is 4 to 97 days depending on the water flow and temperature. The water flow reduces the concentration as does the plants’ absorption of the treatment.

What are the post application restrictions? ​Other than a 30 day restriction on irrigation, there are no restrictions on swimming, drinking, or eating fish from treated lakes . It is prudent practice to close the lake on the day of application (that is, only one day).

How often will the lake require this treatment: ​We anticipate a whole lake early spring application of fluridone and one or two booster treatments within 45-60 days of the initial application. Expected control is for 1 – 2 growing seasons beyond the year of initial treatment. We anticipate that the lake would receive annual monitoring and smaller scale control options in subsequent years.


Based on nearly four decades of experience, NHESP and the EPA have concluded that herbicides, and in particular the recommended herbicide fluridone, are safe for fish, people and non-target plants, and they are specifically safe for M.Lustrica, the endangered snail.

Research by the SBA included conferring with many Berkshire lake managers to learn their experience with herbicides – no adverse consequences were reported. The State agency responsible for protecting marginal species of plants and animals, the Natural Heritage Endangered Species Program, specifically recommended that we use fluridone to control milfoil. Our independent lake expert, Dr. Ken Wagner, confirms the efficacy and safety of herbicides, including fluridone, to control milfoil.

Although some have questioned how fluridone might interact with chemicals previously used more than three decades ago in the Bowl, there is no evidence that any residue from those chemicals still remains in Stockbridge Bowl, as recently determined by sediment samples taken from over 50 locations around the lake and the Outlet. The herbicides widely used nationwide, including fluridone, have been applied in many lakes previously treated by a wide assortment of other herbicides, and we are aware of no reported adverse interactions with fluridone.

In 2016, Cornell Cooperative Extension released a paper confirming the safety of fluridone which included citations from the New York State Federation of Lakes, the Washington State Department of Health, the federal EPA, the Department of the Army, and the Weed Science Society of America.

The SBA will continue to work to preserve Stockbridge Bowl for the future by . simultaneously pursuing the safe application of herbicide, hydro raking and modified dredging.

Additional information:


Dredging. To prevent the areas behind Kwuniikwat Island and down the outlet from becoming a bog, we must dredge a channel through those areas. We are seeking permission from NHESP.