Starry Stonewort

July 17, 2017 lawanda Magazine Columns

        Starry stonewort.  Such a cool name, isn’t it?  It looks kind of nifty too.   I wish there were good things to say about it, but unfortunately starry stonewort is an aquatic invasive species, so here comes the bad news . . .

        Starry stonewort is actually an algae, but it doesn’t look like what you normally would consider algae – the green scummy mats floating on top of the water.  Rather, it is grass-like in appearance with four to six whorls of long branchlets.  What distinguishes it from other grass-like looking plants you might find in the water is that it forms 1/8-inch white, star-shaped bulbils.  Another clue is that if you squish the stems, the green oozes out.  There are native grassy algaes that look similar, but they hold their shape and don’t squish out green goo when the stems are pinched.      The reason starry stonewort is bad is that it forms dense mats of vegetation at the water’s surface that reduces the diversity of aquatic plants, choking out native vegetation.  It also impedes the movement of fish and other animals, even interfering with the spawning of fish.  Mats can get so dense that water flow is reduced and recreational activities like boating, swimming, fishing and waterfowl hunting are impossible.  Starry stonewort can grow up to six feet tall and survives in up to 20 feet of water.  It usually dies back over winter, but can survive if the winter is mild.

        Starry stonewort was first found in Wisconsin in November of 2014 in Little Muskego Lake in Waukesha County.  It has since been found in Racine and Washington Counties, all in the southeastern part of the state.  But guess what?  It’s now been found near Sturgeon Bay, way up in Door County.  One guess as to how it spread up there.  Yep, all it took was ONE boater who didn’t clean their boat properly at the boat landing in one of those three southern counties before taking a vacation in Door County.  Don’t be the guy who makes the same mistake!  See the Clean Boats Clean Waters information.

        You might wonder what is being done to control starry stonewort.  Unfortunately, not much, but not for lack of trying.   It turns out that the chemicals available to kill it are not successful.  The tops of the plants die back, but the bottoms survive and re-grow.  Physical removal is also not working out very well because hand-pulling, raking and suction all break up the plants and any little fragment let loose in the water can grow into an entirely new plant.  There’s always hope for a biological control – an animal, fish or aquatic insect that will eat the plants – but so far none have been found.  Because there is no effective control, it is double important to PREVENT its spread.


Invasive species can spread easily by hitching a ride on boats and other equipment, including trailers, anchors, livewells, buckets and bilges.  Boaters can easily prevent this spread by taking simple precautions.

·         Inspect your boat, trailer, anchor and all equipment and remove all attached plants, animals, mud and debris

·         Drain all water from boats, motors, livewells, bait buckets and other equipment

·         Never move live fish away from a waterbody

·         Dispose of unwanted bait in the trash

·         Buy minnows from a Wisconsin bait dealer, and use leftover minnows only if you will be using them on that same waterbody or if no lake or river water or other fish have been added to the container.

·         Keep drain plugs out during transport

Failure to inspect boats, trailers and equipment at the boat landing is a violation of Wisconsin state law!


If you think you see starry stonewort, the DNR wants to know about it!  Find information about how to report it here: or contact your local DNR office.


The Wisconsin DNR has Early Detection and Response grants to help with removal, control and monitoring of new populations of aquatic invasive species. 


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