Ducks on a wetland in Ladd Marsh Wildlife Area, Oregon
The Ladd Marsh Wildlife Area contains important examples of the Wetlands Strategy Habitat. Photo Credit: Cathy Nowak, ODFW

Wetlands are covered with water during all or part of the year. Permanently wet habitats include backwater sloughs, oxbow lakes, and marshes, while seasonally wet habitats include seasonal ponds, vernal pools, and wet prairies.


Wetlands are identified as a Strategy Habitat throughout Oregon.


Wetland habitats are highly diverse and include the following types:

Alkaline wetlands occur in depressions in more arid areas and are intermittently saturated. An impermeable soil layer prevents water from percolating through the soil, concentrating salts in some areas. Soil salinity varies greatly by soil moisture and type and affects the composition of plant species. Plant species are tolerant of saline conditions due to the concentration of salts by water evaporation. Alkaline wetland vegetation includes salt-tolerant grasses, rushes, sedges, and shrubs such as black greasewood. Examples of this habitat type are found in the Klamath Lake and Goose Lake areas of the East Cascades ecoregion, and in the Northern Basin and Range ecoregion.

Deciduous swamps and shrublands are located in depressions, around lakes or ponds, or on river terraces. They generally flood seasonally with nutrient-rich waters and are dominated by woody vegetation, including willows, hardhack, alder, red osier dogwood, Pacific crabapple, and ash.

Marshes (including emergent marshes) occur in depressions (ponds), fringes around lakes, and along slow-flowing streams, especially in valley bottoms. Marshes are seasonally or continually flooded and have water-adapted plants, such as sedges, bulrushes, spikesedges, rushes, cattails, and floating vegetation. Marshes can have mucky soils, resulting in water with high mineral content and vegetation dominated by herbaceous species, often including wildflowers.

Off-channel habitat, such as oxbow lakes, stable backwater sloughs, and flooded marshes, are created as rivers change course. In these areas, water moves slowly, providing quiet aquatic habitats. These areas provide important rearing habitats for young fish as well as refuge from high flow events, especially during the migration of young salmon to the ocean.

Playas, found in the Northern Basin and Range ecoregion, are sparsely vegetated (generally less than 10 percent plant cover) with grasses, and are surrounded by a ring of shrubs. They are seasonally flooded and have highly saline soil. Plant species composition depends on soil salinity and moisture. Characteristic species include iodine bush, black greasewood, spiny hopsage, saltbush, alkali grass, wildrye, and saltgrass.

Seasonal ponds and vernal pools hold water during the winter and spring but typically dry up during the summer months. Vernal pools occur in complexes of networked depressions that are seasonally filled with rainwater. They host a variety of plant and animal species with unique adaptations. These habitats can be very important for native invertebrate species (e.g., vernal pool fairy shrimp), plants (e.g., big-flowered wooly meadowfoam, Cook’s desert parsley), and amphibians. For example, native amphibians may be able to reproduce in the short timeframes when water is present in seasonal ponds, while invasive non-native bullfrogs cannot. This reproductive advantage can help native amphibians that are sensitive to competition and predation from bullfrogs.

Wet meadows (including montane wet meadows) occur on gentle slopes near stream headwaters, in mountain valleys, bordering lakes and streams, near seeps, in large river valley bottoms, and in open wet depressions among montane forests. They are dominated by tufted hairgrass, sedges, reedgrass, spikesedge, rushes, and wildflowers. Montane wet meadows may have shallow surface water for part of the year, are associated with snowmelt, and are not typically subjected to disturbance events such as flooding.

Wet prairies occur in lowlands, especially in floodplains, whereas wet meadows occur in depressions surrounded by forests and are associated with snowmelt. Wet prairies are dominated by grasses, sedges, and wildflowers.

Ecoregional Characteristics

Blue Mountains

In the Grand Ronde and Baker Valleys, much of the lower elevation wetlands have been drained and converted to agriculture. Most remaining wetlands in this ecoregion are found at higher elevations, although some important valley bottom wetlands occur on private land.

Coast Range

Wetlands are vulnerable to development as more people relocate to be near the coast. Although wetland drainage is now discouraged, continuing development is a threat to some remaining wetlands. In addition, the ecological processes that create coastal wetlands, such as landslides, beaver activity, or logjams blocking streams, often are not compatible with current land uses, especially in more developed areas. Early planning that allows for appropriate riparian buffers along coastal rivers and streams can maintain many important wetland and stream functions, including flood control, water retention and storage, shading, and decreased contaminant inputs. Many of these functions will help to maintain higher stream flows and lower water temperatures in months with less precipitation.

Columbia Plateau

Historical wetlands along the Columbia River have been inundated by reservoirs, while floodplain wetlands along the Umatilla and Walla Walla rivers and other tributary streams have mostly been developed for agriculture. This ecoregion once had extensive springs and vernal pools, many of which have been lost as water tables lowered. Currently, many wetlands in this ecoregion are man-made, such as marshes established along the edges of reservoirs and wetlands created as a result of crop irrigation practices. The Wanaket Wildlife Area, managed by the Confederated Tribes of the Umatilla, is a network of wetlands created through irrigation of pastureland that provides important habitat for many wetland-dependent species. Similarly, ponds on the Umatilla National Wildlife Refuge use runoff from the fish hatchery to seasonally water shallow pools for migrating shorebirds and to provide breeding habitat for amphibians. Irrigation wetlands in this ecoregion can provide important habitat but can also be adversely impacted by runoff containing fertilizers or other chemicals.

East Cascades

The upper Klamath Basin once had an extensive shallow lake and marsh system, but much of that system has been lost due to drainage and conversion to agriculture and urban uses. These changes have contributed to the complex issues surrounding water use and species conservation in the basin. The remaining wetlands in the Klamath Basin support one of the largest concentrations of waterfowl in North America, with over three million ducks and a half-million geese migrating through the basin annually. The area is a critical migratory staging area for 80 percent of all Pacific Flyway waterfowl. In the winter, the Klamath Basin hosts the largest wintering population of Bald Eagles in the continental United States. The Klamath Basin provides Oregon’s only permanent nesting areas for Red-necked Grebes and Yellow Rails.

Klamath Mountains

Most low-elevation seasonal wetlands have been lost to habitat conversion to agricultural, urban, and rural residential uses. Upland activities or altered hydrology impact many remaining wetland habitats. Rare vernal pool wetlands in the Agate Desert near Medford support several rare plant and animal species. These and other vernal pool types of wetlands are formed in areas with unusual topography and soil layering, and are very difficult to replace when ground is leveled for development.

Northern Basin and Range

The Northern Basin and Range ecoregion contains several large, deep freshwater marshes. Significant large wetlands are associated with the large lake basins, including: Abert, Summer, Malheur, and Harney Lakes, and the Warner Basin. However, many of the ecoregion’s smaller historical wetlands have been lost due to conversion or degradation from stream channelization, water diversions, and historical overgrazing. Creation of watering holes for livestock and wildlife has altered the hydrology at many major playas, making them one of the most altered habitat types in the ecoregion.

In some areas, flood-irrigation of private pasture and hay meadows provides important seasonal habitat for migrating and breeding birds. In areas where flood irrigation is being applied to row crops, converting flood irrigation to piped sprinkler systems can improve water quality, reduce sedimentation, and reduce water loss due to evaporation. However, loss of flood irrigation without restoring wetlands in the landscape will negatively affect wetland species now dependent on flooded habitats. Cooperative projects, such as settling ponds designed for cleaning flood irrigation “tail water”, may offer a way to address water quality and wetland habitat issues.

West Cascades

Wetlands are generally in excellent condition, although some areas, such as those located around Mt. Hood, can be impacted by uncontrolled livestock grazing, camping, or off-highway vehicle use.

Willamette Valley

Almost all remaining wetlands in this ecoregion have been degraded to some degree by altered water regimes, pollution, and invasive plants and animals. Wetlands in the Willamette Valley serve important ecological functions for communities, provide habitat for amphibians, turtles, birds, and fish, and offer key bird and fish migratory pathways.

Conservation Overview

Wetlands and wet meadows provide important habitat for migrating and breeding shorebirds, waterbirds, waterfowl, songbirds, mammals, amphibians, and reptiles. Floodplain wetlands and backwater sloughs and swamps are important rearing habitats for juvenile salmon. Wetlands have direct value for people because they improve water quality by trapping sediments and pollutants, recharge aquifers, store water, and reduce the severity of floods. Seasonal wetlands that dry up during the summer provide important ecological functions, such as supporting water quality and sequestering carbon.

Restoration and careful management of wet meadow systems and other wetlands can increase sustainable production of forage for livestock and increase late-season stream flows. Restoration and retention of wetlands, especially those with high water storage potential in arid regions, may help to maintain ground water levels into drought periods.

In general, most wetland habitat loss has occurred at lower elevations and valley bottoms. Many of these wetlands have been drained and converted to agriculture or eliminated due to urban growth.

Limiting Factors and Recommended Approaches

Limiting Factor: Habitat Loss

A high percentage of low-elevation and valley bottom wetlands have been lost or degraded through diking and draining, particularly in the Klamath Mountains and Coast Range ecoregions. In other areas, overgrazing can lead to soil compaction, changes in plant species composition, and spread of invasive plants. In some cases, due to short growing seasons and other factors, degraded wet meadows can be slow to recover if overgrazed. Wetlands in the East Cascades and Northern Basin and Range ecoregions provide vital habitat for migrating shorebirds and waterfowl. Limited or degraded wetland habitat in the Pacific Flyway could potentially have large impacts on bird populations. In the East Cascades ecoregion, significant bird nesting habitat has already been lost. Early season haying in wetland habitats on private and public land can result in poor reproduction of ground-nesting birds due to destruction of nests and direct mortality of young. Many wetlands are lost through urbanization and direct fill for development. Unfortunately, this removes wetlands from locations where the functions they may provide might have the most value for humans and fish and wildlife. Maintaining wetland and surrounding upland habitat near communities can provide: flood water storage and delay capacity, water quality opportunities to allow infiltration and exposure to treat possible contaminants before reaching streams and ground water, temperature regulation when vegetation and shading are retained, safe passage corridors for fish and wildlife, and transportation routes for people.

Recommended Approach

Protect and conserve priority wetland habitat that provides vital breeding habitat for Strategy Species and stopover sites for migrating species (KCI: Barriers to Animal Movement). Identify wetlands that have been altered or lost, and determine their potential for restoration.

Build upon current cooperative efforts to maintain and restore wetlands in partnership with private and public landowners. Cooperative voluntary approaches are important for wetland conservation on private lands. Continue to provide incentives to protect, maintain, or restore wetlands, such as the Wetland Reserve Program offered through the Natural Resources Conservation Service and private mitigation banking. Develop and implement grazing regimes that are compatible with wet meadow conservation objectives. Use cooperative efforts and incentive programs to establish semi-permanent livestock exclusion zones in priority areas. In partnership with landowners, implement later haying dates in critical bird nesting areas (see The Willamette Valley Landowner’s Guide to Creating Habitat for Grassland Birds). Manage beaver populations to contribute to wetland creation and maintenance, when compatible with existing land uses.

Continue successful programs to educate individuals about the function and services provided by wetlands. As part of mitigation programs, restore or create wet prairie, vernal pool, and other seasonal and permanent wetland habitats. Promote awareness of the importance of temporary pond habitat.

Facilitate discussions within communities, including city and county planners, agricultural groups, and forest industries, regarding the functions performed by wetlands. Work with the local planning process to promote the value of maintaining wetlands and habitat corridors, especially along floodways, where they can best function to protect structures, infrastructure, and water quality.

Limiting Factor: Water Availability

Water is extremely limited in much of the Blue Mountains, East Cascades, and Northern Basin and Range ecoregions. As a result, there is competition for water resources, particularly in late summer. Lowered water tables affect wetland habitats. Competition for water harms both ecological and economic goals. Water diversions for other uses change the seasonality of flooding, slow habitat recovery, and increase invasion of non-native grasses. Drought years intensify water shortages.

Recommended Approach

Use cooperative efforts and incentive programs, such as financial incentives for wetlands restoration, water rights acquisition, and wetland mitigation banking, to manage water allocation and wetland habitats. Recognize importance of irrigated wetland habitats, and maintain benefits to species when considering various management and irrigation options. (KCI: Water Quality and Quantity)

Limiting Factor: Degraded Water Quality

Although wetlands have a role in purifying water, water quality is poor in some wetland systems. High temperatures affect water quality in some areas. Non-point source runoff from agricultural and residential areas contains pollutants that can affect water quality and nutrient levels, and these levels may increase as water evaporates throughout the season. High nutrient loads can contribute to toxic algal blooms.

Recommended Approach

Provide economic incentives to decrease and manage the release of potential contaminants, such as fertilizers or pesticides, by controlling the timing of application. Use incentives to promote substitutes that are less toxic to wildlife and break down quickly in the environment. Work with agency, landowner, and business partners to implement the federal Clean Water Act. Promote the creation of stormwater treatment projects, fencing of aquatic habitats to exclude livestock, and restoration of riparian buffers and additional wetlands to increase filtering capacity. Support irrigation systems that conserve, re-collect, and re-use water more effectively, use gray water, and provide shaded treatment areas that can provide cooling and habitat. In the Willamette Valley, adopt critical actions recommended by the Willamette Restoration Initiative on Clean Water, such as: reduce the levels of toxins and other pollutants in the Willamette Basin, provide economic incentives to decrease water pollution, and promote education and outreach programs for homeowners, farmers, and developers. (KCI: Water Quality and Quantity)

Limiting Factor: Invasive Species

Invasive species, such as reed canarygrass, purple loosestrife, and Japanese knotweed, invade and degrade wetlands, thereby displacing native plants, reducing plant community diversity, reducing sources of food for wildlife, and altering water flow and storage function. For example, perennial pepperweed and purple loosestrife have affected important wetlands including Malheur Lake. Invasive, non-native carp can impact wetlands by consuming important plants and by increasing turbidity, disturbing sediments, and altering biological dynamics for sediment-associated plants and animals. Turbidity also contributes to higher water temperatures and lower levels of dissolved oxygen.

Recommended Approach

Emphasize prevention, risk assessment, early detection, and quick control to prevent new invasive species from becoming fully established. Control key invasive plants using site-appropriate tools, such as flooding (reed canary grass), biological control (purple loosestrife), and mechanical treatment including mowing. Use chemical treatment carefully and where compatible with water quality concerns, focusing on spot treatment during the dry season. Adjusting water levels can also help to control invasive carp. Consider screening to control carp. Use revegetation and other means to establish and maintain healthy plant communities that are relatively resistant to invasion and that also meet other land use objectives. (KCI: Invasive Species)

Resources for more information