Fence Rock Lake, Guilford - 2021

2021 aquatic plant survey map of Fence Rock Lake in Guilford, CT

2021 Aquatic Plant Survey of Fence Rock Lake

Transect Data | Water Data

From 2009 to 2016, CAES IAPP surveyed Fence Rock Lake in Guilford, CT to track the invasive plant Brazilian waterweed (Egeria densa). The plant was first detected in 2009 and continued to spread. In 2013, these patches coalesced across nearly the entire cove. The increase in the coverage found the plant growing in deeper water than all previous years. Brazilian waterweed was found on 60 percent of the transect points in 2013.

In 2014, the lake was treated with the herbicide Reward® using a bottom injection technique. In the summer of 2015, a small population of Brazilian waterweed remained, so the lake was retreated. Our 2016 survey and 2017 surveys found no Brazilian waterweed. In 2019, CAES IAPP performed a survey of Fence Rock Lake and found Brazilian waterweed in a small patch by the private beach.

In 2021, CAES IAPP performed another survey to track the reestablishment of the invasive weed in the lake. Brazilian waterweed had spread since the 2019 survey and was found in multiple locations in the lake; however, it was not nearly at 2013 levels, and it was not the most common species found in the lake. Thirteen native aquatic plant species were found in the lake, mostly around the shoreline. The deeper areas had charaphyte, a plant-like freshwater algae, as well as small pondweed (Potamogeton pusillus), slender naiad (Najas flexilis), Brazilian waterweed, and coontail (Ceratophyllum demersum). The most common species in the lake overall was watershield (Brasenia schreberi). An invasive wetland plant, purple loosestrife (Lythrum salicaria), was also found in a few locations on the shoreline. Overall Fence Rock Lake has a diverse abundance of native species, and 2021 conditions were similar to 2019 although Brazilian waterweed continued to spread.

Species recorded in our 2021 survey of Fence Rock Lake
Scientific Names
*Invasive Species
Arrowhead Humped bladderwort Spikerush
Brazilian waterweed* Low watermilfoil Watershield
Bur-reed Primrose-willow Waterwort
Cattail Purple loosestrife* White water lily
Charaphyte Slender naiad Yellow water lily
Coontail Small pondweed  


Other Fence Rock Lake Surveys: 2019, 2017, 2016, 2013, 2012, 2011, 2010, 2009