Lower Mill Pond, Old Lyme

Transect Data | Water Data

     Lower Mill Pond is a 4-acre, man-made pond located in Old Lyme, Connecticut. The pond was created by a dam on Mill Brook, with another impoundment, Upper Mill Pond, situated upstream. Farther upstream is Rogers Lake, which contains populations of the invasive species fanwort (Cabomba caroliniana), variable-leaf watermilfoil (Myriophyllum heterophyllum), and curlyleaf pondweed (Potamogeton crispus). Mill Brook flows from Lower Mill Pond into the Lieutenant River.

     On July 10, 2025, the Connecticut Agricultural Experiment Station Office of Aquatic Invasive Species (CAES OAIS) conducted its first aquatic vegetation survey of Lower Mill Pond. The maximum depth observed during the survey was approximately 3 meters (10 feet), occurring near the dam on the western end of the pond. This area was the only portion of the pond largely free of aquatic vegetation. Due to extremely dense plant growth, only about half of the pond was able to be surveyed. A total of eighteen aquatic plant species were documented, including two invasive species: fanwort and variable-leaf watermilfoil.

     The most abundant species observed were fanwort, variable-leaf watermilfoil, and white water lily (Nymphaea odorata). The next most abundant plants were emergent species, including swamp loosestrife (Decodon verticillatus), bur-reed (Sparganium spp.), and pickerelweed (Pontederia cordata). Great duckweed (Spirodela polyrhiza), a small floating species, and common bladderwort (Utricularia vulgaris) were found in scattered locations throughout the pond.

     Less commonly observed species included coontail (Ceratophyllum demersum), yellow water lily (Nuphar variegata), floating-leaf pondweed (Potamogeton natans), and cattail (Typha spp.). Species observed in only one or two small areas were spiral pondweed (Potamogeton spirillus), Robbins’ pondweed (Potamogeton robbinsii), ribbon-leaf pondweed (Potamogeton epihydrus), spotted pondweed (Potamogeton pulcher), green arrow arum (Peltandra virginica), and watershield (Brasenia schreberi).