Aquatic Weeds by Growth Form
| Growth Form | Where It Grows | Example Species | Primary Concern |
|---|---|---|---|
| Floating (free) | Drifts on the water surface; roots dangle below | Water hyacinth, water lettuce, duckweed, salvinia | Rapid coverage of surface; blocks light and gas exchange |
| Floating (rooted) | Rooted in sediment; leaves rest on the surface | Water lily, watershield, American lotus | Surface coverage in shallows; navigation interference |
| Submerged | Rooted in sediment; entire plant grows underwater | Hydrilla, Eurasian watermilfoil, curly-leaf pondweed, elodea | Dense underwater canopy; oxygen swings; recreation interference |
| Emergent | Rooted in shallow water; stems and leaves rise above the surface | Cattail, alligator weed, common reed (Phragmites), purple loosestrife | Shoreline encroachment; loss of open water; biodiversity loss |
Top Problem Species at a Glance
| Species | Growth Form | Growth Rate | U.S. States Affected |
|---|---|---|---|
| Hydrilla (Hydrilla verticillata) | Submerged | Up to 1 in/day | 30+ |
| Water hyacinth (Eichhornia crassipes) | Floating | Biomass doubles every 6–18 days | 20+ (mainly southern) |
| Eurasian watermilfoil (Myriophyllum spicatum) | Submerged | 1–2 in/day (early season) | 45+ |
| Duckweed (Lemna spp.) | Floating | Biomass doubles every 2–3 days | 50 (native + introduced) |
| Curly-leaf pondweed (Potamogeton crispus) | Submerged | Early-season surge; mid-summer die-off | 45+ |
Quotable Facts
- The USGS Nonindigenous Aquatic Species database catalogs more than 200 non-native aquatic plant species in U.S. waters.
- Hydrilla reproduces through four mechanisms — fragments, turions, tubers, and seeds — making it one of the most difficult aquatic plants to eradicate.
- A single square meter of dense hydrilla can produce 5,000+ tubers, and tubers remain viable in sediment for up to seven years.
- Water hyacinth is listed by the IUCN as one of the 100 worst invasive species in the world.
- Dense submerged weed beds can shift a lake's daily dissolved-oxygen range by 6 mg/L or more between dawn and afternoon — a swing that stresses or kills fish.
- Nutrient loading — particularly phosphorus from agricultural runoff and failing septic systems — is the strongest predictor of aquatic-weed severity in U.S. lakes (see our eutrophication page).
Definitions Journalists Often Need
Related Resources on AquaticWeed.org
- What are aquatic weeds? (full primer)
- Identification guide hub
- Species authority profiles
- Control methods overview
Ten-Year Lake Management Plan: Lake Wingra, WI
Lake Wingra, a 342-acre urban lake in Madison, WI, developed a comprehensive 10-year management plan coordinating the City of Madison, University of Wisconsin, and adjacent neighborhood associations. The plan addressed Eurasian watermilfoil, curly-leaf pondweed, and purple loosestrife through an integrated approach including targeted herbicide treatment, mechanical harvesting, native plant restoration, and public education.
Key outcome: The structured multi-agency planning process secured consistent funding across multiple budget cycles, a key advantage over ad hoc management. Native plant restoration efforts showed measurable progress in designated restoration zones within three years of initiation.
- U.S. Geological Survey — Nonindigenous Aquatic Species Database https://nas.er.usgs.gov/
- U.S. Army Corps of Engineers — Aquatic Plant Information System (APIS) https://apis.erdc.dren.mil/
- USDA APHIS — Federal Noxious Weed List https://www.aphis.usda.gov/plant-pests-diseases/weeds/noxious
- U.S. EPA — Aquatic Pesticide Use & NPDES Permits https://www.epa.gov/npdes/pesticide-permitting
- Pimentel et al. (2005) — Update on environmental and economic costs of invasive species in the U.S., Ecological Economics 52(3): 273–288. https://www.sciencedirect.com/science/article/abs/pii/S0921800904003027
- Rockwell, H.W. (2003) — Summary of a Survey of the Literature on the Economic Impact of Aquatic Weeds, Aquatic Ecosystem Restoration Foundation. https://www.aquatics.org/publications.html
We referenced the biological control pages extensively when evaluating our grass carp stocking proposal. The detail on stocking rates and target species specificity helped us present a credible case to our board.
Karen Ostrowski HOA Lake Committee Chair, MN · Lake Minnetonka associationThe ecological impact section helped our team explain to county commissioners why early intervention matters. The oxygen depletion data alone secured funding for our early-detection monitoring program.
Donna Whitfield State Wildlife Biologist, GA · Okefenokee region