Over the years the Geneva Lake Environmental Agency has conducted several aquatic plant surveys on Geneva Lake. The first one was conducted in 1976 and the most recent one was completed during the summer of 2015. These surveys are the foundation for the aquatic plant management plan. Based upon the type and numbers of plants found in the lake, aquatic plant management strategies are approved or denied when applied for.

The early plant surveys were conducted using the transect methods, with plants identified every given feet along pre-determined transects. During the summer of 2015 a comprehensive survey was conducted using the point intersect method. Points were identified every 50 meters and samples were collected, with plants identified and quantified. A total of 2,685 sites were located by longitude and latitude.

The data from the 2015 survey is still being analyzed but some of the preliminary numbers are interesting. A total of 785 sites were sampled with 653 sites containing vegetation. Although aquatic plants may have been identified as deep as 41.6 ft., most plants were found under 30 ft. (table 1.) The remaining sites were too deep for light penetration and thus plants could not grow. A total of 31 different species were identified. Native species dominated the plant community lake wide.

Coontail (Ceratophyllum demersum) was the most frequently found aquatic plant with a frequency of occurrence of 37.6% and found at 246 sites. Chara ssp., a macro-algae, was the second most abundant with a frequency of occurrence of 33.5 % and found at 219 sites. Close behind as the third most commonly found plant was ditch grass (Ruppia cirrhosa) which had a frequency of occurrence of 32.9% and was found at 215 sites. Of interest was the finding of birds-nest stonewort (Tolypella nidifica), a native plant that is not very common in Wisconsin and not previously identified in Geneva Lake.

A few non-native speices were identified but they were a rather small part of the over-all Geneva Lake plant community. Eurasian milfoil, (Myiophyllum spicatum) had a 24.3% frequency of occurrence and was found at 159 sites. Curly-leaf pondweed (Potamogeton crispus) which is an early season aquatic plant, had a frequency of occurrence of 5% and was found at only 34 sites. Its limited presence may have been due to the time of the survey. Only on five of the 721 sites sampled were either non-native identified as being dominate at the sampled location.

In general, the plant density was low. Average rake fullness, a measure of how many plants were retrieved on the rake, with 1 being sparse and 3 being full, was 1.5. Plant diversity was good as the average number of species found per site was around 2.5.

A means of evaluating the health of a biological community that is commonly used is the Simpson's Diversity Index. This index looks not only at the number of species but also takes into account the abundance of each species. The closer to 1 for the Simpson Index the healthier the community. Based upon the data collected in this survey the Simpson Diversity index for the Geneva Lake’s Aquatic Plant Community was 0.91.

Additional assessment of the aquatic plant survey data is being conducted by Nicholas McCarney, a George Williams College Student. He is investigating where invasive species were found and relating that to species diversity, community richness and past aquatic plant management efforts. Look for his results during summer of 2016.

An Aquatic Plant Management Plan.

A product of the past aquatic plant survey was the preparation of an aquatic plant management plan (see map of recommended management below). This aquatic plant management plan will be reviewed and modified as needed when an assessment of the 2015 survey is completed.

In general, the lake was divided into three separate aquatic plant management areas. The “No Restriction Zone” where it is recommended that there be no restriction on the aquatic plant management strategies if they are compatible with State requirements. The “Native Zone” are areas that have a diverse and healthy plant community and thus no management is needed or recommended unless conditions change. The “Watch Zone” is the largest area in size and includes areas were the plant community may need some minor management but for the most part is relatively stable. An overlay “Riparian Zone” can be located in any one of the other three zones but is restricted to only a 30 ft. wide strip running perpendicular to the shore and extends out into deeper water. This zone is to allow for riparian management of aquatic plants in their swim, mooring or pier areas.

aquatic plant management

Aquatic Vascular Plants Found Geneva Lake, WI 1976 - 2015 - Source: GLEA
Source: GLEA
Plant Species Common Name Found in
1976 1994 2001 2009 2015
Ceratophyllum demersum (L.) Coontail x x x x x
Chara* spp. Muskgrass x x x x
Chara braunii Brauni muskgrass x
Chara contraria Muskgrass x
Drepanocladus spp. aquatic moss x
Elodea canadensis (Michx.) Common waterweed x x1 x x
Elodea nutallii (Planchon.) Slender waterweed x x
Heteranthera dubia (Jacq.) Water stargrass x x x
Juncus pelocarpus brown-fruited rush x
Lemna triscula forked duckweed x
Myriophyllum exalbensence (Fern.) Northern water milfoil x x x1 x
Myriophyllum sibiricum Northern water milfoil x
Myriophyllum heterophyllum (Michx.) Variable milfoil x
Myriophyllum spicatum** (L.) Eurasian water milfoil x x x x x
Najas flexilis (Willd.) Naiad x x x x
Najas guadalupensis southern najas x
Najas marina (L.) Spiny pondweed x
Nitella flexilis Nitella x
Potamogeton amplifolius (Tuckerman) Large leaf pondweed x x x x x
Potamogeton crispus** (L.) Curly leaf pondweed x x x x x
Potamogeton diversifolius (Raf.) Waterthread pondweed x
Potamogeton fresii (Rupr.) Frie's pondweed x x x
Potamogeton foliosus (Raf.) Leafy pondweed x x
Potamogeton gramineus (L.) Variable pondweed x x x
Potamogeton illinoensis (Morong.) Illinois pondweed x x x
Potamogeton nodosus (Poiret.) River pondweed x x x
Potamogeton natans (L.) Floating leaf pondweed x x x x
Potamogeton oakesianus Oaks pondweed x
Potamogeton pectinatus (L.) Sago pondweed x x x x
Potamogeton praelongus (Wulfen) White stem pondweed x
Potomogeton pusillus Small pondweed x
Potamogeton richarsonii Richardsons pondweed x x x
Potamogeton robinsii (Dakes) Fern pondweed x
Potamogeton zosteriformis (Fern.) Narrow leaf pondweed x x x x x
Ranunculus aquatilis White water crowfoot x
Ranunculus longirostris (Godron) Water buttercup x x x
Ruppia cirrhosa Wigeon grass x x x
Schoenoplectus subterminalis Water bulrush x
Stukenia pectinata Sago pondweed x
Stukenia vaginata Sheathed pondweed x
Tollypela intricata Birds nest stonewort x
Utricularia geminiscapa (Benj.) Hidden flower bladderwort x
Utricularia gibba Creeping bladderwort x
Utricularia macrorhiza Common bladderwort x
Utricularia minor Small bladderwort x
Utricularia vulgaris (L.) Bladderwort x x x x
Vallisneria americana (L.) Water celery x x x x x
* an algae, not a macrophyte
** non native species
1 recorded as genus only