The Wetlands of California's Central Valley

Wetlands support an astounding number and diversity of species.  Across the U.S., over one-third of threatened and endangered species live exclusively in wetlands and almost half of all listed species depend on wetlands for at least part of their lives . In California specifically, wetlands are critical for many migratory and resident birds, fish, mammals, reptiles and amphibians. 

California is situated along the  Pacific Flyway , a roughly 10,000-mile bird corridor that stretches from the west coast of South America up to the Arctic. As birds travel varying distances along the Flyway, it is essential that they find stopover sites that provide suitable food and habitat. California’s wetlands offer both and support millions of migrating birds each year. 

For countless native species, our wetlands are more than a temporary stopover. Breeding waterfowl, the threatened giant garter snake and plant species including rushes, sedges and riparian trees rely on wetlands to support them year-round. For all these species, the continued persistence and health of California’s wetlands are essential for survival and recovery. 

Many freshwater wetlands, especially in California, are situated at points where surface water enters underground aquifers, and these wetlands can help to refill the aquifers. Wetlands also act as natural  water filters . As water flows through wetland vegetation, sediment that was previously suspended settles, becoming part of the ground layer so that the water flowing out of the wetland is less cloudy. Water that has lower sediment content is generally less toxic, which benefits people who consume or use the naturally detoxified water and filter-feeding animals like mussels and clams, which thrive in clearer waters.

In low-elevation areas, like California’s Central Valley, wetlands are also key for flood protection. Wetlands have high water storage capacity and their vegetation slows the speed of flood waters, so in times of high rainfall, wetlands are a natural form of stormwater detention. In coastal areas,  wetlands offer a buffer from wind and wave action  that result from storm surges and help to reduce erosion.  This will become increasingly important  as California continues to grapple with climate change and sea level rise.

Since time immemorial, Native American Tribes in California have used wetlands and other waters to support their cultural, spiritual, ceremonial, and traditional rights. Wetlands continue to serve these purposes today, including by providing important nursery grounds for juvenile salmon, which are of inestimable cultural importance to several tribal communities. 

Hiking, birdwatching, biking, hunting, paddle-boarding, photography, and kayaking are just a few of the outdoor activities that take place in wetlands and their surrounding trails. Wetlands are also utilized as outdoor classrooms for children to experience place-based education programming.

In the Central Valley, wetland wildlife refuges are important for efforts to ensure equitable access to nature. California has established a  goal of conserving 30% of natural lands and water by the year 2030  and expanding equitable outdoor access and recreation for all Californians is a key part of this initiative. Expanding equitable outdoor access involves increasing access to outdoor recreation for  disadvantaged communities , including those that have been disproportionately affected by environmental pollution. For many disadvantaged communities, refuges in the Central Valley are the closest public lands and provide wonderful recreational opportunities. Protecting and expanding these wetland refuges could help ensure that all Californians have meaningful access to public lands. 

California’s wetland acreage has declined more than in any other state, with  only 10-percent of historical wetlands remaining . The Central Valley once contained an extensive network of wetlands. In the mid-1800’s, seasonal and year-round Central Valley wetlands began being drained and diked so they could instead serve as agricultural lands. Today, only a tiny remnant of the Valley’s historical wetlands remains.

Wetland losses in the Central Valley have been particularly harmful because of the key role Central Valley wetlands play for migratory birds travelling the Pacific Flyway. These wetlands are the  most important stopping point along the Flyway  for five million migratory waterbirds, which make up 60% of the Pacific Flyway waterfowl population and 20% of all migratory waterbirds in North America. California’s migratory bird populations have  declined in the last 100 years , in part due to the loss of Central Valley wetland habitat. Wetland losses in the Central Valley have devastated other species, including the giant garter snake, which is now listed as threatened under the Endangered Species Act.

Although the CVPIA has helped to protect California’s wetlands, the federal government has not fulfilled its legal obligations and supplied the refuges with the required amounts of water. The U.S. Bureau of Reclamation was supposed to deliver full water supplies to the refuges each year after 2002 but has never done so. Inadequate water deliveries remain one of the biggest threats to these precious Central Valley wildlife refuges.

Climate change will exacerbate the refuges’ water-supply challenges. California is experiencing reduced snowpack and more frequent and severe droughts, which make it even harder for the refuges to get the water they need to support migratory birds, giant garter snakes, and other wildlife.

The refuges also face financial challenges. The CVPIA Restoration Fund, which pays for water deliveries and infrastructure to support the refuges, has never been fully funded and is now being further threatened by proposed federal policy changes. More than a quarter century after passage of the CVPIA, some refuges lack infrastructure that is necessary for receiving water deliveries and no funding sources have been identified to fill these gaps.

Finally, while the refuges are protected from development, other wetlands in the Central Valley continue to be lost to urban and agricultural development. The Trump administration made this problem much worse by eliminating important Clean Water Act protections for some wetlands. The refuges alone cannot provide adequate food and habitat for all the birds that migrate through the Central Valley and protecting the Valley’s diverse mosaic of wetland habitats is essential.