Regional Aquatic Weed Guide by EPA Ecoregion
Different parts of the United States face different aquatic weed challenges. This guide maps the most common nuisance species to EPA Level III ecoregions and USDA Hardiness Zones so you can anticipate what you're likely to encounter in your area.
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Understanding the Framework
EPA Ecoregions define areas with similar ecosystems — climate, soil, vegetation, and water characteristics. They're useful for aquatic weed management because plant distribution follows ecological boundaries rather than political ones.
USDA Hardiness Zones indicate minimum winter temperatures. Many aquatic invasive species are limited by cold tolerance — water hyacinth thrives in Zone 8+ but is killed by winter in Zone 6.
For the full EPA ecoregion framework and maps: EPA Ecoregions | National Aquatic Resource Surveys Ecoregions
Northern Lakes and Forests
Region: Great Lakes states, Upper Midwest, northern New England USDA Zones: 3–5 Key characteristics: Cold winters, clear lakes, acidic to neutral water
Priority Species
| Species | Severity | Notes |
|---|---|---|
| Eurasian Watermilfoil | Severe | The #1 aquatic invasive in this region — outcompetes native milfoils |
| Curly-Leaf Pondweed | Severe | Grows under ice; die-back fuels summer algae blooms |
| European Frog's-bit | Moderate | Expanding in Great Lakes basin |
| Starry Stonewort | Moderate | Expanding; persistent bulbils |
| Purple Loosestrife | Moderate | Biocontrol has reduced impact significantly |
| Phragmites | Moderate | Invasive form displaces native wetland plants |
| Flowering Rush | Low-Moderate | Expanding in the region |
Species NOT typically a problem here
Water hyacinth, water lettuce, giant salvinia, hygrophila — these tropical/subtropical species are killed by winter in Zones 3–5.
North Central Hardwood Forests
Region: Southern Great Lakes, Upper Midwest (southern WI, MN, MI, IA) USDA Zones: 4–6 Key characteristics: Productive agricultural landscape, nutrient-rich lakes, moderate winters
Priority Species
| Species | Severity | Notes |
|---|---|---|
| Eurasian Watermilfoil | Severe | Widespread and aggressive |
| Curly-Leaf Pondweed | Severe | Major problem in nutrient-rich lakes |
| Duckweed | Moderate-Severe | Nutrient loading from agriculture drives blooms |
| Coontail | Moderate | Native but can become excessive |
| Phragmites | Moderate | Invasive hybrid cattail also a concern |
| Cattails | Moderate | Hybrid T. × glauca especially aggressive |
Northeastern Highlands
Region: New England, northern Appalachians, Mid-Atlantic uplands USDA Zones: 4–6 Key characteristics: Forested watersheds, acidic to neutral lakes, rocky substrates
Priority Species
| Species | Severity | Notes |
|---|---|---|
| Eurasian Watermilfoil | Severe | Primary aquatic invasive concern |
| Phragmites | Severe | Dominates coastal and roadside wetlands |
| Cabomba | Moderate | Expanding in soft-water lakes |
| Bladderwort | Low-Moderate | Native, common in acidic waters |
| Watershield | Low | Native; nuisance when excessive |
Atlantic Coastal Pine Barrens
Region: Coastal Mid-Atlantic (NJ Pine Barrens, Long Island, Cape Cod) USDA Zones: 6–7 Key characteristics: Sandy soils, acidic water, coastal influence
Priority Species
| Species | Severity | Notes |
|---|---|---|
| Phragmites | Severe | Dominates tidal and freshwater wetlands |
| Cabomba | Moderate | Thrives in soft, acidic water |
| Bladderwort | Low-Moderate | Common in acidic ponds and bogs |
Southeastern Plains
Region: Interior Southeast — Piedmont to Coastal Plain (VA, NC, SC, GA, AL, MS, LA, east TX) USDA Zones: 7–9 Key characteristics: Warm, humid, nutrient-rich water, long growing season
Priority Species
| Species | Severity | Notes |
|---|---|---|
| Hydrilla | Severe | The #1 aquatic invasive in the Southeast |
| Water Hyacinth | Severe | Doubles population every 2 weeks in summer |
| Alligator Weed | Moderate-Severe | Federal Noxious Weed; dense floating/shoreline mats |
| Creeping Water Primrose | Moderate-Severe | Aggressive shoreline expansion |
| Floating Heart | Moderate | N. cristata especially aggressive |
| Duckweed | Moderate | Year-round in warm climate |
| Hygrophila | Moderate | Aquarium escapee, shade tolerant |
Southern Coastal Plain
Region: Gulf Coast and Florida USDA Zones: 8–11 Key characteristics: Subtropical to tropical, year-round growing season, very high nutrients
Priority Species
| Species | Severity | Notes |
|---|---|---|
| Hydrilla | Severe | Grows year-round; epicenter of US hydrilla invasion |
| Water Hyacinth | Severe | Year-round growth; enormous biomass |
| Water Lettuce | Severe | Federal Noxious Weed; year-round in frost-free areas |
| Giant Salvinia | Severe | Can form mats several feet thick |
| Hygrophila | Moderate-Severe | Federal Noxious Weed |
| Duckweed / Watermeal | Moderate | Year-round |
| Elephant Ear | Moderate | Ornamental escapee |
| Alligator Weed | Moderate | Both aquatic and terrestrial forms |
Mississippi Alluvial Plain
Region: Mississippi Delta, lower Mississippi River floodplain USDA Zones: 7–9 Key characteristics: Rich alluvial soils, nutrient-loaded water, seasonal flooding
Priority Species
| Species | Severity | Notes |
|---|---|---|
| Hydrilla | Severe | Widespread in bayous and oxbow lakes |
| Water Hyacinth | Severe | Blocks navigation in waterways |
| Giant Salvinia | Severe | Major problem in bayous and reservoirs |
| Alligator Weed | Moderate-Severe | Common along waterways |
Western Gulf Coastal Plain
Region: East Texas, Louisiana coast USDA Zones: 8–9 Key characteristics: Warm, humid, bayou and coastal prairie ecosystems
Priority Species
| Species | Severity | Notes |
|---|---|---|
| Giant Salvinia | Severe | Critical invasive — multi-foot thick mats |
| Water Hyacinth | Severe | Widespread |
| Hydrilla | Severe | Expanding |
Central Corn Belt Plains / Western Corn Belt Plains
Region: Midwest agricultural heartland (IL, IN, OH, IA, MO, KS, NE) USDA Zones: 5–7 Key characteristics: Agricultural runoff, nutrient-rich water, farm ponds
Priority Species
| Species | Severity | Notes |
|---|---|---|
| Eurasian Watermilfoil | Moderate-Severe | Common in lakes and reservoirs |
| Duckweed / Watermeal | Moderate-Severe | Agricultural nutrients drive explosive growth |
| Curly-Leaf Pondweed | Moderate | Common in nutrient-rich lakes |
| Coontail | Moderate | Native, common in farm ponds |
| Cattails | Moderate | Aggressive expansion in farm ponds |
| Filamentous Algae | Moderate-Severe | Nutrient-driven |
Marine West Coast Forests / Willamette and Central Valleys
Region: Pacific Northwest (WA, OR, northern CA) USDA Zones: 7–9 Key characteristics: Mild winters, moderate summers, clear water
Priority Species
| Species | Severity | Notes |
|---|---|---|
| Egeria | Severe | Major invasive in Pacific NW and California waterways |
| Parrot Feather | Moderate-Severe | Water garden escapee, expanding |
| Purple Loosestrife | Moderate | Present but biocontrol has helped |
Central California Valley
Region: Sacramento and San Joaquin Valleys USDA Zones: 9–10 Key characteristics: Warm summers, irrigation canals, agricultural water systems
Priority Species
| Species | Severity | Notes |
|---|---|---|
| Egeria | Severe | Major problem in Sacramento-San Joaquin Delta |
| Water Hyacinth | Severe | Year-round growth in mild climate |
| Parrot Feather | Moderate | Common in irrigation systems |
Species That Cross Regional Boundaries
Some species are found everywhere and don't follow regional patterns:
| Species | Distribution | Notes |
|---|---|---|
| Duckweed | All 50 states | Severity proportional to nutrient loading |
| Coontail | All 50 states | Native; nuisance when excessive |
| Elodea | All 48 contiguous states | Native; rarely needs treatment |
| Cattails | All 50 states | Hybrid form most aggressive |
| American Pondweed | All 48 contiguous states | Valuable native — manage selectively |
| Planktonic Algae | Universal | Most common pond complaint everywhere |
| Filamentous Algae | Universal | Shallow, clear, nutrient-rich ponds |
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Natural Waterscapes — Expert Aquatic Plant Identification & Treatment EPA ecoregion data from EPA Eco-Research. Species distribution from USGS NAS and USDA PLANTS Database.