Identify Wisconsin Lake Weeds
Before you remove anything, identify it. Wisconsin's permit rules treat native and invasive plants differently, and two of the most common invasives have native lookalikes that are easy to confuse from the surface. These seven specimen plates cover what you're most likely looking at along a Wisconsin shoreline.
Eurasian watermilfoil
invasiveMyriophyllum spicatum
- Feathery leaves in whorls of 4 around the stem
- Each leaflet divided into 12 or more pairs of thin segments
- Stem runs 3 to 10 feet, often reddish and limp out of water
Restricted invasive. Hand removal is permit-exempt statewide; chemical treatment needs an NR 107 permit.
Identification only. Permit rules are on the DNR permit page.
Curly-leaf pondweed
invasivePotamogeton crispus
- Submersed leaves 0.5 to 3.5 in long, alternating along the stem
- Reddish-green, wavy, finely serrated edges, like lasagna noodles
- Reddish-brown stem, 1 to 3 feet
Restricted invasive. Hand removal is exempt; mechanical harvesting or an NR 107 herbicide are the other options.
Identification only. Permit rules are on the DNR permit page.
Coontail
nativeCeratophyllum demersum
- Dark green, stiff, bushy leaves in whorls of up to 12
- Each leaf forked with small teeth, rough to the touch
- No roots; floats or anchors loosely in soft bottom
Protected native. Removal beyond the 30-foot exempt corridor needs an NR 109 permit.
Identification only. Permit rules are on the DNR permit page.
Elodea (waterweed)
nativeElodea canadensis
- Slender branching stem, narrow leaves in whorls of 3
- Smooth leaf edges, unlike its invasive lookalikes
- Rooted in the lake bottom, unlike free-floating coontail
Protected native, same permit rule as coontail. Confirm ID before pulling; small spines or extra leaflets per whorl point to an invasive lookalike instead.
Identification only. Permit rules are on the DNR permit page.
Native watermilfoil
nativeMyriophyllum sibiricum
- Looks like Eurasian watermilfoil at a glance
- 10 or fewer leaflet pairs per leaf, versus 12 or more
- Stiffer stalks, not limp or reddish out of water
Easy to mistake for the invasive lookalike. Confirm the leaflet-pair count before pulling; removing native milfoil without an exemption is a violation even by mistake.
Identification only. Permit rules are on the DNR permit page.
Duckweed
nativeLemna minor
- Tiny round-oval floating fronds, one root each
- No true stem; often carpets calm bays by late summer
- Reproduces fast, so a small patch becomes a mat quickly
Protected native. Usually a skim or net job at the pier; larger or repeated removal should be confirmed with the DNR first.
Identification only. Permit rules are on the DNR permit page.
Filamentous algae
nativeCladophora, Spirogyra, Pithophora spp.
- Thread-like strands forming floating mats, not a rooted plant
- Cottony (Cladophora), slimy bright green (Spirogyra), or steel-wool coarse (Pithophora)
- Usually worst near a dock in calm, nutrient-rich water
Native algae, not a plant. DNR's practical advice is to rake floating mats near a dock and cut nutrient runoff; confirm larger or repeated removal with the DNR first.
Identification only. Permit rules are on the DNR permit page.
Once you know what you're looking at, check whether you need a permit and compare removal methods.