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The Aquatic Invasive

Starry Stonewart

Aquatic invasive species are non-native plants or animals that are introduced into a body of water. Since these species are not native, they can quickly and easily thrive in the introduced environmental, many times uncontrollably. This becomes a problem as the species continue to grow exponentially and outcompete native aquatic life, resulting in the introduced species to take over. Invasive species are a large concern for aquatic environments and we work hard in preventing the spread of known and unknown invasives into our lake. 

Starry stonewart is a species of green macro-algae that is native along the west coast of Europe and Japan. It spreads fast and creates dense mats of algae, disrupting native plants, fish spawning habitats, and boat motors. Unintentionally introduced into the Great Lakes Chain through contaminated ballast water on a cargo ship, starry stonewort became a serious concern during the fall of 2018 when it was found in a lagoon on the southeastern shore of Geneva Lake. During the summer of 2019, two small patches of starry stonewort were found in the lake near the lagoon, continuing to multiply and take over the lake from there.

The present management strategy on Geneva Lake is to contain and control the spread of starry stonewort to other locations within Geneva Lake. Major components of that management effort are:

Education: working with the Clean Boats Clean Waters program, to inform boaters and lake users of the efforts they need to take to help reduce the spread of aquatic invasive species

Monitoring: conducting lake-wide aquatic plant surveys for quantitative and qualitative assessments of the lake environment

Protection: maintaining a healthy, biodiverse plant community to protect against the establishment of non-native species


The GLEA conducted a modified point intersect (PI) aquatic plant survey during the summer of 2021. The 2021 sub PI survey focused on access points to Geneva Lake, Trinke Lagoon, and the area surrounding. Education of boaters to clean their boats, trailer, bilges, bait buckets, live wells, and anchors as they move between lakes as well as within Geneva Lake is vital in controlling the spread of aquatic invasive species. During the summer of 2021, the GLEA worked in coordination with other organizations to purchase a portable boat cleaning station that rotates through the five public launch sites which will continue this summer. Additionally, the Clean Boats Clean Waters initiative trains staff in working with boaters on understanding their obligation in reducing the spread of invasive species. 

It is illegal to leave a launch site with vegetation hanging on your vehicle, boat, or trailer.  Please make sure to follow the required boat cleaning before you launch as fines are applicable. See the Wisconsin Department of Natural Resources web site for information on boat transportation and bait laws. 




We spent time at the starry stonewort colony site scuba diving to monitor populations. Starry stonewort is an invasive plant that was first seen in Geneva Lake in 2018. These plants are solely male and spread by releasing bulbils, that act as seeds, growing wherever they land. Movement such as hand-pulling is believed to actually stir up these seed-like bulbils and cause more damage by promoting spreading. Through routine dive checks on known population sites we are able to see how these plants are growing. While starry stonewort hasn't gone away, we haven't seen too much growth and believe our native species have been doing a good job at keeping this invasive plant at bay. 



An aquatic plant  survey conducted at the lake's access sites did not find any new populations of starry stonewort at any launch sites as of the end of July.  Several new populations of starry stonewort were found in the general area of the the "deep water" site located to the east of Trinke. Whether these sites are new or were missed last year is unknown. During the last week of July a six man dive team hand pulled starry stonewort from the "deep water" site and areas east were starry stonewort was identified as being present in the aquatic plant survey.  A small amount of starry stonewort was also pulled from just outside of the Trinke lagoon. 


The Dive Guys with an afternoon's worth of hand pulled starry stonewort.

Geneva Lake WI July 29, 2021 

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