Conflicting Reports

News Analysis: CLA Report Contradicts Effectiveness Of Third-Party Herbicide Treatment Study

Two studies focusing on Chautauqua Lake found that herbicide treatments removed weeds from large areas near the shorelines. The lake is pictured from the village of Mayville. P-J photos by Jordan W. Patterson

Chautauqua County’s Memorandum of Agreement regarding Chautauqua Lake could be on the verge of becoming a Memorandum of Disagreement.

An independent study of Chautauqua Lake paid for by Chautauqua County and a report by Racine Johnson paid for by the Chautauqua Lake Association agree that herbicide treatments removed weeds from large areas near Chautauqua Lake’s shores.

That point is just about the only point of agreement between the two studies.

Princeton Hydro, the county’s independent third party consultant whose report was released in September, deemed herbicide treatments on Chautauqua Lake to be successful in their intent and that adverse impacts were minimal. Racine Johnson, on the other hand, released its report in December and writes that its 2019 survey of plant life in Chautauqua Lake shows a lake littoral system in peril.

Racine Johnson’s study states aquatic weed growth was within normal growth patterns near the center of the lake and was progressively sparse moving south toward Jamestown.

“However, this fall other stakeholders accepted the news reports, internet posts and a third-party report that the management of aquatic macrophytes by the application of aquatic herbicides, south of Long Point, on Chautauqua Lake in 2019, was a success and beneficial,” the Racine Johnson report states. “We agree, the application of the herbicides 2,4-D and endothall on May 15-17, 2019, were successful in removing macrophytes from large areas of the lake’s littoral zone (where plants grow). Conversely, we do not agree that this almost total plant removal in those areas was beneficial, but rather it was detrimental to the health of the lake’s ecosystem. We have not seen an adequate evaluation of the efficacy of this major 2019 management event on Chautauqua Lake. To not recognize or acknowledge the results of this management decision is a serious deficiency of indispensable information essential to the management of Chautauqua Lake.”


Both reports agree there was drift of herbicides outside the treatment area. Princeton Hydro’s report noted that some drift is to be expected in a lake environment and recommends that any future herbicide use maintain the same sampling locations and dates to allow for comparisons to accurately measure drift and create a more accurate statistical model for drift.

“The appearance of higher herbicide concentration under the longer-scale, post-treatment conditions indicates that these products may have had a potential residual impact,” the Princeton Hydro study states. “However, based on the plant density/biomass data and statistics, such residual impacts were negligible on native species but might have impacted the invasive species curly-leaf pondweed in the control areas. However, even this potential impact is confounded by the fact that curley-leaf pondweed begins to die off naturally as the seasons move from spring through summer and water temperatures increase.”

Racine Johnson’s analysis, meanwhile, paints a more insidious effect of herbicide drift. The area not treated with herbicide is 4.3 miles northwest of its paired treatment area.

“This clearly suggests the drift and concentration of 2,4-D was vast and basin-wide, likely contributing to the massive indiscriminate defoliation of the macrophytes in the south basin,” Racine Johnson stated in its report.


Princeton Hydro’s post-treatment study found that total weed biomass declined in all treatment zones with a marked reduction in Eurasian milfoil and curley leaf pondweed while indicating a reduction of native plants in two drift zones. Even noting that unexpected impact in two zones, Princeton Hydro officials wrote that the herbicide treatment worked as expected, with invasive species decreasing and native plants increasing.

“Finally, it should be noted that the adjusted floristic quality index showed a significant increase from pre- to posttreatment conditions,” Princeton Hydro officials wrote. “Thus, while the targeted invasives species declined, overall community diversity and value (native species) increased with the treatments.”

Racine Johnson somewhat confirms Princeton Hydro’s analysis, stating that 27 species of plants were found in Chautauqua Lake in 2019, a decrease of three species from 2003 to 2008.

The main difference between the two reports is Princeton Hydro’s view of Eurasian milfoil and curly-leaf pondweed as invasive species that needed to be eradicated and Racine Johnson’s view of Eurasian milfoil and curly-leaf pondweed as important species to be found in the lake. Additionally, Racine Johnson’s latest study argues that there is actually no weed problem in the lake because there were more plants in the lake in the 1970s and 1980s than there are now.

Racine Johnson officials argue that even if Eurasian milfoil and curly-leaf pondweed did need to be controlled, the two non-native plants targeted by herbicides are controlled better by moths, weevils and caddis flies.

“The two dominate non-native species are Potamogeton crispus (curly-leaf pondweed) since 1937 and Myriophyllum spicatum (Eurasian watermilfoil) since 1975,” Racine Johnson scientists wrote. “These two non-native species are an integral component of the macrophyte species community in Chautauqua Lake and have not caused a decrease in native species richness over this long-time span (Table 3), nor is there any data showing an increase in biomass in recent years. … Without a measurable increase in macrophyte mass in recent years from the historical records, the case, scientifically and economically, for removing plant growth by herbicides is weak. Even weaker is the misguided drive to eliminate plants that are an integral part of, and provide vital ecosystem functions just because they are termed non-native. Watermilfoil and curly-leaf pondweed are long-term residents of Chautauqua Lake and maintain this healthy lake ecosystem as naturalized species.”

According to the state Department of Environmental Conservation, Eurasian milfoil and curly-leaf pondweed are classified as invasive species that are the subject of corrective measures. Eurasian milfoil, in particular, is listed as prohibited in New York waters despite its presence in New York for more than 70 years.

“Responses must be developed not only for new, or relatively new (aquatic invasive species) problems, but for AIS problems that have persisted for decades as well,” the state DEC’s 2015 Aquatic Invasive Species Plan states. “For example, aquatic plant species such as water chestnut, Eurasian watermilfoil, and curly-leaf pondweed have caused significant adverse impacts to both the ecology and recreational enjoyment of New York state waterbodies for over 50 years.”


Last spring, most towns and villages that line Chautauqua Lake as well as the non-profit agencies that deal with the lake signed on to the Chautauqua Lake Memorandum of Agreement.

One of the document’s main tenets is collaboration amongst the agencies who signed to achieve a weed management consensus that includes a centralized lake authority, science-based decisions, integration of management methods, use of herbicides as a management tool, nutrient management through aquatic plant management and the invasive versus naturalized status of Eurasian milfoil and curly-leaf pondweed.

In other words, the agreement paved the way for herbicide use, with conditions, and set up a framework to create an integrated Chautauqua Lake management plan. One way to do that was setting up a central lake authority that would be a sole direction setter for lake maintenance decisions. The agreement also included a clause that signatories wouldn’t sue each other, as had happened in the past.

The agreement says nothing about the agencies contradicting each other publicly.

That means, as the Chautauqua Lake Watershed and Management Alliance prepares for the future with a new executive director and a new Memorandum of Agreement, old questions are coming back to the forefront.

On whose science will decisions be based?


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