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Pacific Southwest, Region 9

Serving: Arizona, California, Hawaii, Nevada, Pacific Islands, Tribal Nations

Wetlands of the Pacific Southwest

Wetlands Quick Finder
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National Links

National EPA Wetlands Site

Hydrology and Hydrography
of the Tulare Basin

Full Report (PDF) (136pp, 45M)

Report Text (PDF) (92pp, 32M)

List of Figures (PDF) (8pp, 742K)

List of Tables (PDF) (18pp, 766K)

List of Appendices (PDF) (11pp, 4M)

Photo of a wetlands creek

Regional Wetlands and Related Habitats

The Pacific Southwest Region supports many types of wetlands, from alpine wet meadows to coastal tidal marshes. Each wetland type provides a unique suite of physical and biological functions. Depending on the type and location, our regional wetlands provide:

  • a home for fish and wildlife, including critical habitat for endangered species
  • enhanced water quality
  • ground water recharge areas
  • flood control
  • shoreline buffering and erosion control
  • recreation

EPA’s Pacific Southwest Region has lost well over 90% of its wetlands in the last 150 years, more than any other region of the country. Although most of these losses occurred prior to 1972, when Congress enacted the Clean Water Act, the region’s remaining wetlands continue to be threatened by human activities, especially suburban and agricultural development. Seasonal wetlands and vernal pools are particularly at risk because they occupy relatively flat terrain that is easy to develop. Even if they are not filled, wetlands may be degraded by improperly controlled runoff, non-native invasive species, and fragmentation.

EPA’s section 404(b)(1) Guidelines recognize wetlands as having special ecological characteristics and a strong influence on environmental health. They, therefore, afford them a high-level protection by classifying them as "special aquatic sites." Examples of some other special aquatic sites in Region 9 are coral reefs, mudflats, and vegetated shallows.

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Some of Region 9’s wetlands are shown below.

Wetlands of the Pacific Southwest
a vernal pool

Vernal Pools
A vernal pool during the wet season near Merced, California
National Vernal Pools site
palm oasis in the Mojave

Desert Springs
Desert spring in the Coachella Valley near Palm Springs, California
waterfowl habitat in winter and hayfield in summer

Seasonal Farmed Wetlands
Seasonal wetlands along San Pablo Bay in Sonoma County, California, provide waterfowl habitat in winter and are hayfields in summer.
Meeker slough, a tidal marsh

Tidal Marsh
Tidal marshlands at Meeker Slough, near EPA's lab in Richmond, California
fresh water wetland Viansa winery

Fresh water marshes & sloughs
Fresh water wetlands at the Viansa Winery near Sonoma, California

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