Aquatic Nuisance Species

A rooted, shallow water plant. Grows in thick mats and shades out natives. Stunted fish can occur as heavy cover reduces predation. Late summer die-off causes alga blooms, reducing oxygen needed by fish. Common in Minnesota and Wisconsin waters. Stems reddish-brown to whitish-pink, 1/8-1/4 inch diameter and grows to 5 feet. Leaves deeply divided, soft, feather like, about 2 inches long. Flowers reddish and small; held several inches above water when plant blooms. Infestations often started by plant fragments growing into new plants. Chemical/mechanical control costly, often unsuccessful; also kills native species. Grows best on soft mud bottoms in waters with moderate nutrient levels.
Photo courtesy Bonnie Alexander

Grows soon after ice out, deprives later-growing plants of nutrients. Forms thick surface mats that inhibit boating and swimming. In summer, mats increase small-fish escape cover and decrease predation. Dies off late summer and reduces cover for small fish in shallows. Gamefish move to shallows to feed on them and are vulnerable to overharvest. Plant stems 1-3 feet long. In summer, leaves oblong, reddish-green, fine-toothed edges, 3 inches long. Chemical control costly, often ineffective. Mechanical control dislodges seed pods that float to new areas.