Institute for Wetland & Environmental Education & Research

Wetland Primer
How Are Wetlands Identified?

Some wetlands are readily identified by their obvious wetness throughout the year or by their unique vegetation. Since only 26% of the plants that grow in wetlands are obligate hydrophytes (unique to wetlands and waterbodies), most of the plants found in wetlands grow in uplands (non-wetlands) to varying degrees. This makes it important to look beyond plants to identify those wetlands not dominated or otherwise characterized by obligate hydrophytes. The majority of wetlands may require examination of soil properties to confirm their wetland status, since they are dry for much of the growing season. These latter wetlands are usually wet in early spring and during the "non-growing seasons".

For federal regulatory purposes, jurisdictional wetlands are identified by considering vegetation, soil characteristics, and other signs of wetland hydrology: positive indicators of hydrophytic vegetation, hydric soil, and wetland hydrology are required, with few exceptions. For hydrophytic vegetation, most of the dominant plants in the plant community must have a wetland indicator status of facultative or wetter (see discussion above under Hydrophytic Vegetation). For hydric soil, applicable field indicators must be observed or soils must be inundated for more than 2 weeks during the growing season in most years (every other year on average). Indicators of wetland hydrology include: 1) rusty-coatings along root channels (oxidized rhizospheres indicative of a plant bringing oxygen to its roots under anaerobic soil conditions), 2) water-stained leaved (blackened leaves due to prolonged inundation), 3) water marks (black marks on tree trunks caused by extended flooding - common on trees of deep swamps in the South), 4) silt marks (silt deposited on vegetation by floodwaters), 5) sediment deposits and drift lines (water-deposited materials), 6) observed inundation during the growing season, and 7) observed soil saturation within 12 inches of the soil surface during the growing season.

The U.S. Army Corps of Engineers wetland delineation manual provides the guidance for identifying jurisdictinal wetlands. States have traditionally relied on vegetation to identify wetlands subject to their regulations, but recently have either adopted the federal approach or developed tiered methods to identify wetlands by first considering vegetation and when necessary, considering other characteristics such as hydric soil properties and other hydrologic indicators. Contact applicable regulatory agencies for details.

Useful sources of wetland information to aid in their identification include National Wetlands Inventory (NWI) maps published by the U.S. Fish and Wildlife Service, county soil survey maps published by the U.S.D.A. Natural Resources Conservation Service, and state and local wetland maps. The NWI maps use standard U.S. Geological Survey topographic maps as a base and show the approximate boundaries and types of wetlands and deepwater habitats. NWI maps may be ordered by calling 1-800-USA-MAPS.

Access to map data may be available for some areas through the Internet Access "Wetland Inactive Mapper" at the FWS's web site - The maps are compiled through photointerpretation techniques with limited field checking. More conspicuous wetlands are readily depicted, while certain forested wetlands (especially drier types and evergreen types) and other drier-end wetlands are more conservatively mapped (e.g., many are not shown and boundaries are inexact). Soil survey reports provide information on soil types and locations of various soils in the subject county. This information is also generalized, but in most cases, has been compiled from extensive field investigations. The combination of NWI maps and soil survey data present the best picture of where wetlands are likely to be, without making field inspections. State and local wetland maps may also be available from applicable conservation/environmental agencies.
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