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204 assessment of climate change in the southwest united statesChanges in reservoir storage will affect lake recreation, just as changes in streamflowtiming and amounts affect such activities as rafting and trout fishing. Changes in thecharacter and timing of precipitation and the ratio of snowfall to rainfall will continue toinfluence winter recreational activities and tourism (Ray et al. 2008).Sacramento-San Joaquin Bay Delta VulnerabilitiesBox 10.2The functioning of the Sacramento–San JoaquinBay Delta is the most critical water issuein California and arguably the most pressingwater problem in the United States. This confluenceof California’s two major riversystems—the largest estuary on theWest Coast—is used as a natural conveyancefacility to move water for 25million people. Seventy percent ofthe state’s water moves southwardfrom the Sacramento River, throughthe delta, to canals that supply bothCentral Valley agriculture and themunicipal and industrial demands inthe Los Angeles metroplex.The delta has been substantiallymodified by humans from its originalstate and is highly vulnerable toshutdown due to both physical andlegal issues (CDWR 2005; NRC 2010,2011, forthcoming). Within the delta,approximately sixty islands sit belowor near sea level and are protectedby 1,300 miles of aging levees. Theselevees are subject to failure from sealevelrise, subsidence, freshwaterflooding, earthquakes, and poor leveemaintenance (Mount and Twiss2005) . Failure of the levees from anycause could cause a massive influxof sea water from the San FranciscoBay into the freshwater delta, thuscurtailing the movement of freshwaterthrough the delta. Disruption ofthe flow could cost upwards of $30billion and require many years to fix (Benjaminand Assoc. 2005). Both the State Water Projectand the federal Central Valley Project are at risk(CDWR 2009b; Lund et al. 2010).Figure 10.2 Map of Sacramento-San Joaquin Bay Delta.Reproduced with permission from the Public Policy Institute ofCalifornia (Lund et al. 2007, Figure 1.1).