Eurasian water-milfoil (Myriophyllum spicatum)
An emergent, herbaceous aquatic plant, Eurasian watermilfoil, usually extends 3 to 10 feet, but can reach as much as 33 feet in length. The stems are reddish-brown to whitish-pink. It forms dense mats on the surface of water bodies, and new plants that may emerge from each node on a stem root on contact with mud. Regenerates mostly from rhizomes, fragmented stems, and axillary buds that develop throughout the year. Eurasian watermilfoil can be found in nearly 400 WI lakes.
More information here: https://dnr.wi.gov/topic/Invasives/fact/EurasianWatermilfoil.html