History of VLM in Raquette Lake

A Short History of Variable Leaf Milfoil (Myriophyllum heterophyllum) in Raquette Lake

Variable Leaf Milfoil (VLM) is an invasive aquatic plant that has been in Raquette Lake for decades, possibly as long as 80 years.  Anecdotally, long-lived residents say that VLM has been in Raquette Lake as long as they can remember. VLM is native to water bodies in the southern U.S.. Up until 2015, DEC basically classified VLM as a non-native plant, which means it was not listed as an invasive plant in DEC’s regulations.  However, following several cases in New York (e.g. Upper Saranac Lake) where a new introduction of VLM resulted in explosive growth that damaged native plant communities and the lake’s ecosystem, the DEC added VLM to its list of regulated prohibited invasive plants.  

The first known comprehensive survey of Raquette Lake’s aquatic plant community dates back to a 1933 survey conducted by NYS.  A world renowned plant taxonomist at the time, W. C.  Muenscher, was hired to do the survey. Mr. Muencher found thirty-nine species of aquatic plants in Raquette Lake. VLM was not one of them.  

The first survey that focused on VLM was done in 2004 by 25+ volunteers of RLOPA (RLPF’s predecessor). After training by Adirondack Park Invasive Plant Program (APIPP), DEC, and Darian Freshwater Institute staff, RLPOA volunteers surveyed a very large percentage of the shoreline and the first map of VLM in Raquette Lake was created. RLPOA then started our program of benthic matting. The 2016 APIPP survey validated RLPF’s VLM map, and because they were a recognized agency, we have used their map as our VLM mapping basis ever since. Our volunteers continue to survey the shoreline annually to track the VLM population and to monitor for new invasive species. You can view a map showing the general locations of VLM in Raquette Lake here.

The only other comprehensive survey of Raquette’s plant community occurred in 2016 when the  APIPP surveyed the entire shoreline of Raquette Lake (Report link).   Only twenty-six species were identified during this survey even though the area covered was larger than that examined in 1933.  Additionally, only 12 of the plant species found in 2016 were also found in 1933.  It should be noted that in 2015 staff from SUNY Cortland surveyed selected areas of Raquette Lake and found 29 species.

APIPP’s survey found 93 weed beds, totaling 418 acres, in Raquette Lake, the Marion River and South Inlet. VLM was found in 31% of the 93 weed beds for a total of 299 acres. It should be noted that 120 acres of VLM were located in the South Inlet (66 acres) and Marion River (54 acres). Where VLM was found, its average density was around 20% of the total plant community. In only three weed beds was the density greater than 50%.

The reason for the decline in species from 1933 to 2016 is unclear. Differences in methodologies,  analyst expertise and changes in species taxonomy certainly must have played a role.  It’s clear, too, that lakes are dynamic, and that over a period of 83 years some changes in the lake’s plant community are expected. 

For reasons experts don’t fully understand, VLM has not posed the same threat to Raquette Lake’s ecosystem that it has in other lakes.  Nonetheless, we carefully monitor Raquette’s VLM population, and when it shows signs of expanding or interfering with recreation or navigation, we have harvested it. We are fortunate to have on the RLPF board our resident expert on VLM, Pat Deyle, who, with the help of volunteers, annually surveys the shoreline of Raquette Lake to track its VLM population.