Rivers and streams provide great value, as well as some risks, to California.
- California’s almost $4 trillion economy—including its $60 billion agricultural industry—relies heavily on rivers for water supply. Rivers generate 20% of the state’s electricity and are hubs of recreational activity.
- Rivers and streams sustain commercially, culturally, and ecologically significant fisheries. These include salmon, steelhead trout, and remarkably diverse freshwater fish, many found nowhere else in the world.
- Most of California’s cities are built along rivers and streams, which puts them at high risk for flooding. A large statewide flood could cause $1 trillion in economic damages—greater than any projected earthquake.
California has many different types of rivers and streams, which create diverse habitats for numerous aquatic species.
- The state’s more than 180,000 miles of rivers and streams include large meandering rivers like those in the Sacramento Valley, the braided multi-channel rivers of southern California, headwater streams in the Sierra Nevada, and the dry washes of the desert interiors.
- Flows change dramatically from season to season and year to year, corresponding to California’s highly variable precipitation. The largest flows on most rivers are associated with atmospheric river storms or, in desert regions, intense summer thunderstorms.
- The state is a global freshwater biodiversity hotspot, with over 1,700 species of freshwater animals and plants. Of the more than 130 freshwater fish species in California, over half are found only within the state.
Dams provide vital services, but they also contribute to the declining health of rivers and streams
SOURCES: This map is based on a figure originally created by Lucy Andrews. Dam locations and primary purpose from the National Dam Inventory, US Army Corps of Engineers. Flow lines from NHDPlus V2, Environmental Protection Agency.
NOTES: Dams are colored on the map based on their primary purpose—including water supply, hydropower generation, and flood control—although many of the state’s larger dams perform multiple functions. “Other” in the legend includes dams whose primary function is debris control, ponds for watering stock, irrigation, or fish and wildlife ponds.
Water diversions, dams, levees, and a changing climate are impacting river and stream health.
- Since European contact, California’s waterways have been fundamentally altered. Approximately half the water that previously flowed in rivers and streams is now used to support cities and farms. In some regions, the amount diverted is as high as 80%. Some rivers that used to flow year-round now only flow in the winter through early summer, due to water depletion.
- Most of the more than 1,500 large dams and tens of thousands of smaller instream barriers are necessary to sustain the state’s economy and protect it from floods. But these dams have fragmented California’s rivers, altering the natural flows and disrupting the movement of water, sediment, nutrients, fish, and wildlife.
- Thousands of miles of rivers have been lined with levees or other flood control structures, including more than 1,400 miles in the Central Valley alone. These structures help protect cities and farms from flooding yet also disconnect rivers from floodplains that serve as rearing habitat for salmon, recharge floodwaters into aquifers, and replenish soil nutrients.
- Changes to rivers and streams have led to worsening ecosystem health, including the degradation of water quality, the spread of invasive species, and the decline of native fish and wildlife populations.
Major challenges lie ahead, but progress is being made.
- Though California’s watercourses cannot be restored to pre-European-contact conditions, the state is working with federal and local partners to protect rivers and streams and the many services they provide, including clean and reliable water supplies, hydropower, fisheries, recreation, and flood protection.
- The recent removal of four dams on the Klamath River was a big step to improve river health and represents the largest restoration project of this kind in the nation’s history.
- Today’s management approaches should incorporate the altered conditions of California’s rivers and the impacts of the changing climate. To be successful, the state could shift away from a narrow focus on endangered species and toward improving ecosystem health at the watershed scale in ways that benefit both native species and human uses.
- Meeting this challenge will depend upon California’s ability to increase the pace and scale of habitat restoration in critical watersheds throughout the state. The state should remove barriers so that wildlife can move up and down watersheds and onto floodplains and restore more natural fluctuations in flows to cue fish migration, move sediment and nutrients, and sustain restored habitat.
Improving ecosystem health will require restoring some natural fluctuations in flow
SOURCE: Ted Grantham, Jeffrey Mount, Eric Stein, and Sarah Yarnell. Making the Most of Water for the Environment: A Functional Flows Approach for California’s Rivers, PPIC.
NOTES: The figure depicts flow with time in a hypothetical Central Valley river. The green shading shows current flows; the yellow shading shows historical flows before the construction of dams and diversions. Native plants and animals are adapted to large seasonal changes in flow that cue and/or aid migration, create access to habitat, and create physical changes in rivers, such as by refreshing spawning gravels. Reducing diversions or letting water flow into rivers from reservoirs at key times can boost flows to improve ecosystem functions (blue shading).
Topics
Freshwater Ecosystems Paying for Water Safe Drinking Water San Joaquin Valley Water Supply Water, Land & AirLearn More
Making the Most of Water for the Environment: A Functional Flows Approach for California’s Rivers
Commentary: California Needs Bold New Strategies to Save What’s Left of Its Freshwater Species
Improving the Health of California’s Freshwater Ecosystems
Access to Safe Drinking Water in California
Climate Change and California’s Water
Water Use in California’s Environment
