Mapping Montana Wetlands
A Guide to Montana’s Statewide Wetland and Riparian Mapping Framework
Introduction
Montana’s statewide Wetland and Riparian Mapping Framework provides a digital map layer of wetlands, deepwater habitats and riparian areas across the state. The layer is part of the Montana Spatial Data Infrastructure , co-stewarded by the University of Montana, the Montana State Library, and the Montana Department of Environmental Quality.
The following story map introduces standard wetland mapping nomenclature used in Montana’s statewide wetland and riparian mapping layer and offers brief descriptions of habitat and function for each wetland type present in Montana.
This mapping product is an estimation of where wetlands and riparian features may be on the landscape, and is not intended to be used as an actual representation of on-the-ground conditions for regulatory purposes. All wetland and riparian mapping represents photo interpretation from aerial imagery.
Slide left to view Montana's statewide wetland and riparian mapping layer Slide right to view aerial imagery
Wetland mapping follows the US Fish and Wildlife Service definition and classification system.
There is no universally accepted definition for wetlands, with established definitions varying based on their intended use. The term generally refers to land supporting vegetation and soils that reflect permanent or periodic saturation or inundation. The most widely recognized definitions refer to three characteristics of wetlands: hydrology, hydric soils and hydrophytic vegetation. The National Wetlands Inventory (NWI) and Montana Statewide Wetland and Riparian Mapping Layer follow the US Fish and Wildlife Service (FWS) definition below:
"Wetlands are lands transitional between terrestrial and aquatic systems where the water table is usually at or near the surface or the land is covered by shallow water... Wetlands must have one or more of the following three attributes: (1) at least periodically, the land supports primarily hydrophytes; (2) the substrate is predominantly undrained hydric soil; and (3) the substrate is nonsoil and is saturated with water or covered by shallow water at some time during the growing season of each year" [1].
For more information on NWI Wetland Mapping, follow this link .
NWI Wetland Classification System
Wetland classification systems are used to group wetlands based on features such as vegetation, water source, function, or landscape position. A standardized classification system provides consistent units to inform use, management, and planning decisions.
Montana's Statewide Wetland and Riparian Mapping Framework adapts the standard NWI wetland classification system to map form using a system of alphanumeric codes. The codes are structured hierarchically, from System and Subsystem at the broadest levels to Classes, Subclasses, and Water Regime at finer scales [2].
In Montana, the riverine system includes all wetlands and deep-water habitats contained within a channel except wetlands dominated by trees, shrubs, persistent emergent vegetation, emergent mosses, or lichens [1].
Riparian zones are vegetated areas that are affected by an adjacent waterbody's surface and subsurface hydrology [3].
In Montana, the palustrine system includes all wetlands dominated by trees, shrubs, or herbaceous vegetation. Small, shallow ponds and adjacent non-vegetated shore features are also included in the palustrine system [1].
The lacustrine system includes wetlands and deepwater habitats such as lakes, reservoirs, and large ponds. Adjacent shoreline features are also included in the lacustrine system [1].
Fluctuating water levels of the Ruby Reservoir, Montana
Explore Wetland and Deepwater Systems in Montana
Click below to view mapped features in each system. Click on individual polygons in the map viewer to see wetland code.
Montana is home to many wetlands and waterbodies that provide critical habitat and important ecological functions.
Scroll down to see examples of characteristic Montana wetlands and their corresponding NWI wetland codes.
Prairie Potholes
Wetland codes: PEM1A, PEM1C, PEM1F
Prairie potholes occur in Montana within intermontane glaciated valleys and in the northeastern great plains [4, 5].
Great plains prairie potholes occur primarily in northern Montana from the Blackfeet Reservation to the North Dakota border [5].
These glacially formed depressional lakes and wetlands characteristically occur in thick concentration across the landscape.
Intermontane prairie potholes occur more sporadically across the landscape in glaciated valleys of the Northern Rockies such as the Flathead and Blackfoot Valleys [6].
Great plains and intermontane prairie potholes support a number of essential ecosystem services such as surface water storage, nutrient cycling, carbon sequestration, groundwater recharge, and flood control [7, 8, 9].
Blackfoot River
Wetland codes: R3UBH, R3USA, R3USC, Rp1FO, Rp1SS, Rp1EM
A free-flowing, fifth order tributary of the Columbia River, The Blackfoot River spans 212 river-kilometers (132 river-miles) from its headwaters along the continental divide near Rogers Pass, Montana to the confluence with the Clark Fork River just east of Missoula, Montana [10].
In addition to providing drinking water, agricultural irrigation, and iconic recreation opportunities, the Blackfoot remains a source of critical habitat connectivity between the Crown of the Continent Ecosystem and the Selway-Bitterroot and High Divide ecosystems to the south.
The Blackfoot supports a diverse array of riparian systems.
Riparian systems along the Blackfoot include higher elevation riparian forests, sub-alpine montane riparian shrublands, and herbaceous wet meadows.
The Blackfoot River and its tributaries support over 40 listed species of concern including westslope cutthroat trout and bull trout. Grizzly bear, gray wolf, Canada lynx, wolverine, sandhill crane, and trumpeter swan are just a handful of the many wildlife species that rely on the greater Blackfoot watershed [10, 11].
Lower Perennial Rivers of Montana
Wetland Codes: R2UBH, R2USA, R2USC, Rp1FO, Rp1SS, Rp1EM
The Milk River and the Powder River are two of Montana's characteristic lower perennial rivers.
The Milk River flows from the confluence of the Middle and South Forks of the Milk River north of Browning, Montana to the confluence with the Missouri River just downstream of Fort Peck.
The Powder River flows northeast into Montana from the confluence of the Middle and North Fork of the Powder River near Kaycee, Wyoming to the confluence with the Yellowstone near Terry, Montana.
The Milk and Powder rivers are characterized by their low gradient and well developed floodplains. Riparian stands of cottonwood and willow are common along both rivers.
In Montana, these lower perennial systems are generally considered warm water fisheries supporting fish like walleye, catfish, and largemouth bass.
Beaver Influenced Wetland Complexes
Wetland codes: PEM1Bb, PEM1Eb, PEM1Fb, PSS1Bb, PSS1Eb, PSS1Fb
Beaver influenced wetlands occur adjacent to ponds, small lakes, streams, and rivers throughout the state of Montana [12].
Existing dam building capacity throughout Montana modeled by the Montana Beaver Restoration Assessment Tool (BRAT)
Beaver (Castor canadensis) build dams that create, extend, and maintain wetlands.
These beaver-influenced ponds and wetlands trap sediment and organic material, and provide flood control during periods of high flow.
By creating and maintaining their own habitat, beavers in turn support habitat heterogeneity for macroinvertebrates, amphibians, birds, and mammals, including bats [13].
In the statewide wetland and riparian mapping layer, beaver influenced wetlands are given a lower-case b modifier.
Bowman Lake
Wetland codes: L1UBH, L2ABG
Bowman Lake is the third largest lake in Glacier National Park with a surface area of 7 square kilometers (2.7 square miles) and a depth of 77 meters (253 feet).
Located on the west side of the park, Bowman Lake functions as an important headwater source for the Flathead River Basin.
The lake’s oblong shape is a remnant of the enormous ice age glaciers that once poured down from the surrounding cirque, scoured out the linear U-shaped valley, and deposited an end moraine that now dams the lake.
Like many lakes in Glacier National Park, Bowman is oligotrophic with productivity limited by cold temperatures, extreme depth, and mineral deposits from the surrounding rock [14].
Native fish species present in Bowman Lake include westslope cutthroat trout, bull trout, and mountain whitefish [15]. Populations of native fish have been compromised due to historic practices of stocking lakes with non-native sportfish species.
Emergent Marsh
Wetland codes: PEM1C, PEM1F
Emergent marshes are widespread throughout Montana from foothill to upper montane elevations [16].
Emergent marsh habitat in Montana based on 2017 Landcover
In Montana, this system typically occurs in depressions along slow-flowing streams and rivers, adjacent to or in ponds and prairie potholes, and as fringes around lakes or oxbows.
Seasonally flooded marshes (PEM1C) are dominated by graminoids and sedges, while semi-permanently flooded marshes (PEM1F) are dominated by cattails and bulrushes.
These systems are influenced by wet-drought year climatic cycles.Over the course of one 10 to 20 year cycle, these wetlands will typically move through a dry marsh, regenerating marsh, degenerating marsh, and open water phase.
Emergent marshes support several species of concern in Montana including several species of bats, birds, reptiles, amphibians, invertebrates, and vascular plants [16].
Rocky Mountain Subalpine-Montane Fens
Wetland codes: PEM1D, PEM1B, PSS1D, PSS1B
Rocky mountain subalpine-montane fens occur sporadically throughout western Montana.
This map broadly outlines where subalpine-montane fens may occur in Montana based on landcover.
Fens are among the most biodiverse and ecologically important of all wetland types. These unique wetlands are defined by groundwater-driven hydrology and an accumulation of peat.
Peat accumulation occurs when prolonged saturation of the substrate creates anaerobic conditions in the soil.
Oxygen deficiencies in the soil slow down the process of decomposition so that the rate of organic matter production becomes greater than the rate of decomposition.
Peatlands host over 10,000 years of post-glacial history due to the slow rate of peat accumulation and decomposition of organic matter.
Fens provide a number of critical environmental processes including significant carbon sequestration, water purification, and flood regulation.
In Montana, mountain fens provide habitat for a number of rare and uncommon bryophytes, vascular plant species, mammals, mollusks, and insects.
Herbaceous communities are typically dominated by sedges, spikerushes, and rushes; willow and birch dominate woody communities; and among bryophytes, sphagnum mosses are the most common [17].
Explore the interactive map to learn about habitat and function of Montana's wetlands and waterbodies.
Click individual features below to read habitat and function descriptions for each wetland type in Montana. For more information on the Statewide Wetland and Riparian Mapping Framework, visit our website.
ArcGIS Web Application
