Manitook Lake, Granby


2004 Aquatic Plant Survey Map of Manitook Lake

(1.5 MB, .pdf format*)

Transect Data (234 KB, .pdf format*) | Water Data

Manitook Lake is naturally fed by a stream that enters at the north end after running through an active sand and gravel pit. Water flows out of the lake through the long, shallow channel to the south.  A now-closed municipal landfill sits on a wooded slope above the east side of the lake, and homes have been built on the western side. Residents in this area are members of a lake association that prohibits public use of the lake but permits boating, including use of boats with motors. Association members have been concerned that aquatic plants could interfere with recreational use of the lake and asked that it be surveyed in 2004. One resident said septic systems serving homes on the west side of the lake may be inadequate and that lawn fertilizer may raise nutrient levels in the lake water above natural levels. The 56.9-acre Manitook Lake supports a diverse community of aquatic plants, including at least 23 species.  No single species was dominant, but many species were abundant.

Most abundant in the main body of the lake were Potamogeton robbinsii, Ceratophyllum echinatum, Vallisneria americana and Najas guadalupensis. In the southern end of the lake, Najas guadalupensis was most abundant, and Nymphaea odorata grew abundantly along the sides. Less abundant species in the southern part of the lake were Nuphar odorata, Elodea nuttallii, Nymphoides cordata, Ceratophyllum echinatum, Vallisneria americana, Potamogeton amplifolius and Potamogeton robbinsii.  Both Nymphaea odorata sub-species (spp.) odorata and spp. tuberosa occurred on the west side of this area.

The northern end of the lake was less diverse.  Ceratophyllum echinatum was most abundant although it was found primarily in small patches. Nymphaea odorata was most abundant in shallow water along the edges. An invasive species, Myriophyllum heterophyllum, occurred in large patches in this area, as did Vallisneria americana, Elodea nuttallii, Potamogeton amplifolius and Potamogeton crispus. Smaller patches or individual plants of Utricularia gibba and Najas guadalupensis also were recorded. Several patches of Myriophyllum tenellum, a species of special concern in Connecticut, were recorded in this area as well, forming a thick carpet in water 2 m deep in one location.

The bottom drops steeply on the lake’s east side; no floating-leaved species occurred in the area, and submerged species occurred more sparsely than in other parts of the lake. Vallisneria americana and Ceratophyllum echinatum were most abundant, and Potamogeton robbinsii occurred in deeper water. Much of the middle of the lake was too deep to sample.


            A narrow channel flowing from the southern end of the lake supported dense populations of Myriophyllum heterophyllum, with Nymphaea odorata, Brasenia schreberi and Nuphar variegata along the sides of the channel. Smaller patches or individual plants of Elodea nuttallii, Ceratophyllum echinatum, Potamogeton amplifolius, Potamogeton robbinsii, Potamogeton pusillus, Potamogeton epihydrus, Najas guadalupensis, Vallisneria americana, Utricularia vulgaris and Utricularia purpurea also were recorded.

Find Common Plant Names

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Species recorded in our 2004 survey of Manitook Lake. Click on plant to view herbarium mount. (invasive species in bold)


Callitriche heterophylla

Ceratophyllum echinatum

Eleocharis sp.

Elodea nuttallii

Isoëtes sp.

Myriophyllum heterophyllum

Myriophyllum tenellum

Najas guadalupensis

Potamogeton amplifolius

Potamogeton crispus

Potamogeton epihydrus

Potamogeton gramineus

Potamogeton pusillus

Potamogeton robbinsii

Potamogeton zosteriformis

Utricularia gibba

Utricularia purpurea

Utricularia vulgaris

Vallisneria americana


Brasenia schreberi

Nuphar variegata

Nymphaea odorata ssp. odorata

Nymphaea odorata ssp. tuberosa

Nymphoides cordata

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