By James E. Cloern, Jane Kay, Wim Kimmerer, Jeffrey Mount, Peter B. Moyle, and Anke Mueller-Solger
If we farmed the Central Valley or managed water supplies for San Francisco, San Jose or Los Angeles, we might think that fresh water flowing from the Sacramento and San Joaquin rivers through the Delta to San Francisco Bay is “wasted” because it ends up in the Pacific Ocean as an unused resource. However, different perspectives emerge as we follow the downstream movement of river water through the Delta and into San Francisco Bay.
If we were Delta farmers or administered Contra Costa County’s water supply, we would value river water flowing through the Delta because it repels salt intrusion (Jassby et al. 1995) and protects water quality for drinking, growing crops and meeting other customer needs.
If we were responsible for protecting at-risk species, we would value river water flowing through the Delta to the Bay and ocean because it stimulates migration and spawning of native salmon, delta smelt, longfin smelt, and splittail while reducing the potential for colonization and spread of non-native fish (Brown et al. 2016). River flow reduces toxic selenium concentrations in clams eaten by sturgeon, splittail, and diving ducks (Stewart et al. 2013), and it delivers plankton and detritus to fuel production in downstream food webs (Sobczak et al. 2002).
If we managed a Bay Area storm water district or sewage treatment plant, we would value water flowing from the Delta into the Bay because it dilutes and flushes such urban contaminants as metals, microplastics, and nutrients (McCulloch et al. 1970).
If we directed restoration projects around the Bay, we would value water flowing from the Delta into the Bay because it brings sediments required to sustain marshes that otherwise would be lost to subsidence and sea level rise (Stralberg et al. 2011; Schoellhamer et al. 2016). Sediment input from rivers also sustains mudflats (Jaffe et al. 2007) used as habitat and probed for food by more than a million willets, sandpipers, dunlins and other shorebirds during spring migration (Stenzel et al. 2002).
If we fished the Pacific for a living, we would value river flow into the Bay because it carries cues used by adult salmon to find their home streams and spawn (Dittman and Quinn 1996), it brings young salmon to the sea where they grow and mature, and it creates bottom currents that carry young English sole, California halibut and Dungeness crabs into the Bay (Raimonet and Cloern 2016) where they feed and grow before returning to the ocean.
If we liked to romp along the shore or served on the California Coastal Commission we would value rivers flowing to sea because they supply the sand that keeps California’s beaches from eroding away (Barnard et al. 2017).
Finally, if we were among those who want to conserve California’s landscape and biological diversity, we would value river water flowing to the sea because it creates one of the nation’s iconic estuaries and sustains plant and animal communities found only where seawater and fresh water mix (Cloern et al. 2016).
Is the fresh river water that naturally flows through the Delta to San Francisco Bay and on to the Pacific Ocean “wasted”? No. The seaward flow of fresh water is essential to farmers, fishers, conservationists, seashore lovers, and government agencies that manage drinking water supplies, restore wetlands, protect coastlines, and clean up sewage and storm pollution. Wasted water to some is essential water to others.
James Cloern is a senior research scientist with the U.S. Geological Survey. Jane Kay is an independent science writer. Wim Kimmerer is a research professor with the Romberg Tiburon Center for Environmental Studies. Jeffery Mount is a senior fellow with the Public Policy Institute of California. Peter B. Moyle is a UC Davis Professor Emeritus of fish biology and an associate director of the Center for Watershed Sciences. Anke Mueller-Solger is the Associate Director for Projects at the U.S. Geological Survey.