Southern cove of Lake Quonnipaug in Guilford, CT

Lake Quonnipaug, Guilford - 2020

2020 aquatic plant survey map of Lake Quonnipaug in Guilford, CT

2020 Aquatic Plant Survey Map of Lake Quonnipaug

Transect Data | Water Data

Lake Quonnipaug is a 99-acre waterbody located in Guilford, CT. There is a public boat launch at the northern tip of the lake and a public beach on the western shore. The shoreline is moderately developed with private residences.

CAES IAPP performed the fourth full survey of Lake Quonnipaug in 2020. Previous full surveys were performed in 2004, 2010, and 2015, but CAES IAPP has also done state listed species and treatment effectiveness monitoring on the lake for many years. The 2020 survey found the same four invasive species found in previous years: fanwort (Cabomba caroliniana), Eurasian watermilfoil (Myriophyllum spicatum), variable-leaf watermilfoil (Myriophyllum heterophyllum), and curlyleaf pondweed (Potamogeton crispus). Herbicide treatments have greatly reduced the abundance of the invasive species in all areas of the lake except the southern cove. This survey was performed before the 2020 treatment. The northern end by the boat launch was free of invasive species post-treatment. The southern cove has abundant fanwort and curlyleaf pondweed as well as both watermilfoils.

Lake Quonnipaug has a very diverse assemblage of aquatic plants. Aside from the four invasives, 26 native aquatic plant species were found in 2020. This is similar to previous years. The most abundance species are Robbins’ pondweed (Potamogeton robbinsii) and large-leaf pondweed (Potamogeton amplifolius). Robbins’ pondweed is a relatively low-lying plant that rarely impedes navigation; it is present throughout the littoral zone of the lake. The water lilies, watershield (Brasenia schreberi), white water lily (Nymphaea odorata), and yellow water lily (Nuphar variegata), were also abundant in the coves. Most of the lake is navigable; however, the southern cove becomes impassible due to floating muck islands and invasive fanwort. While Lake Quonnipaug has persistent invasive aquatic plants, aside from the southern cove, the lake has a healthy abundance of diverse native species.

Lake Quonnipaug 2020 Report

Species recorded in our 2020 survey of Lake Quonnipaug.
Scientific Names
*Invasive Species
Arrowhead Eelgrass Pickerelweed Variable-Leaf watermilfoil*
Berchtold's pondweed Eurasian watermilfoil* Primrose-Willow Watershield
Cattail Fanwort* Quillwort Waterwort
Clasping-Leaf pondweed Flat-Stemmed pondweed Robbins' pondweed Western waterweed
Common bladderwort Floating-Leaf pondweed Slender naiad White water lily
Common duckweed Great duckweed Small pondweed Yellow water lily
Coontail Large-Leaf pondweed Snailseed pondweed
Curly leaf pondweed* Leafy pondweed Swamp loosestrife

Other Lake Quonnipaug Surveys: 2015, 2010, 2004