Persicaria amphibia (aka Polygonum amphibium). Water smartweed, aka many other common names. http://wisplants.uwsp.edu/scripts/detail.asp?SpCode=PERAMP http://www.fs.fed.us/wildflowers/plant-of-the-week/polygonum_amphibium.shtml http://www.swcoloradowildflowers.com/Pink%20Enlarged%20Photo%20Pages/persicaria%20amphibia.htm

You really can't put too much trust in Internet photos for species that are sold for aquariums, because they are often entirely different from the same species in the wild. Leaves for Limnobium spongia can be floating, or emergent, and plants could easily be found on mud if water depth varies. Since I've never seen L. spongia, I'm not stubborn about the ID :). However, you might find the following link useful, since it provides a detailed description of that plant - Limnobium spongia from FNA.

It looks more like Rhynchospora, than Scirpus to me. The Scirpus that I see in Arkansas tend to be larger plants, with more numerous, and often drooping florets. I did check BONAP here, and saw that Scirpus hattorianus can have a similar appearance in your area. You can also click this link to see what Rhynchospora are found in the Ontario area. If you open a floret and check the achene under magnification, Rhynchospora will have achenes that are crowned with a tubercle (looks like a triangular-shaped cap), and Scirpus lacks that feature.

Lots of plants are native in Wisconsin that survive wet sites. The key is periodic flooding as most will not tolerate being wet all the time. Some that tolerate lowlands and wet in spring are: silver maple, river birch, speckled alder, nannyberry viburnum, black willow, sandbar willow, hackberry, swamp white oak, American linden, buttonbush, elderberries, tamarack, ironweed, red milkweed, blue flag iris ect. Some of these will tolerate more wetness than others. Speckled alder can practically grow in standing water it is so water tolerant. Bald cypress will take water well too and does survive in S.E. Wisconsin.