The Bay-Delta 
San Francisco’s iconic Golden Gate Bridge overlooks the ocean edge of the Bay-Delta Ecosystem—a complex system of rivers, riparian habitats (where land and rivers meet) and inland and coastal estuaries. It is the heart of California’s water system. The area encompasses the west slope of the Sierra Nevada Mountains, south slope of the Siskiyou Mountains, east slope of the Northern Coastal Range, and the San Francisco Bay-Delta. The Delta provides habitat for hundreds of species of fish, birds and other wildlife and protects one of nature’s most miraculous migrations—the run of Pacific salmon from spawning grounds in the upper reaches of cold-water rivers to the saline oceans and back again. Climate change is significantly shifting the hydrology of this region, tremendously impacting both humans and wildlife.
A Home for Threatened & Endangered Species
Pacific salmon migrate between fresh and salt water every season. Fish that migrate together—based on latitude and genetic characteristics—are called runs and often behave differently. The threatened spring-run and endangered winter-run Chinook salmon primarily exist in only two locations. The “species of concern” fall-run Chinook are found in multiple rivers.
Twelve of the original 29 indigenous Delta fish species are either extinct or endangered. The Delta smelt, once an extremely abundant species, is now endangered. Its decline is viewed as an indicator of the deteriorating condition of the region.
All ten California Wild and Heritage trout are in the territory. The threatened Central Valley steelhead is a unique rainbow trout that migrates to the ocean. The threatened green sturgeon forages along estuaries and bays and returns to freshwater pools to spawn. Additional threatened and endangered species that use this habitat include Swainson’s Hawk, California least tern, California black rail and clapper rail, Smith's blue butterfly, salt marsh harvest mouse, northwestern pond turtle, tiger salamander, tidewater goby, California freshwater shrimp, and imperiled vernal pool species.
Climate Change Threats
In the past, a heavy winter snowpack in the mountains slowly melted through the spring and was coupled with healthy spring rain to ensure that a steady supply of fresh cold water coursed through the ecosystem. Today with climate change, there is less snow and more rain in the winter, and less rainfall later in the season, when it is needed most. This changed precipitation pattern, combined with more droughts, creates dry, low-flow, and warmer conditions in California’s rivers. Without healthy, cold-water rivers, habitat that is critical for the survival of the Central Valley Steelhead, spring-run and winter-run salmon has greatly declined.
In addition, climate change has impacted the political climate in the region. Reduced water availability due to climate change has been misleadingly blamed on water restrictions for Endangered Species Act protections. Scientific studies have exposed the truth, but the media and common knowledge remain mired in myth rather than science.
Needed Conservation Measures
This ecosystem’s endangered species won’t survive climate change without a shift in California’s water management. Currently, massive dams, canals and pumps move water north to south for California’s exploding population—expected to exceed 50 million by 2050. Unrealistic human demands on water must be addressed. Water management must focus on efficiency, conservation, run-off recovery, ground water management, storage and other innovative strategies. Conservation easements, land acquisitions and corridor protections for streams are also key strategies. The current Sierra Mountain meadow restoration is one example—improving water storage in upper elevations to increase flows later in the season. (To learn more about upstream conservation measures that
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