Nearly 75 percent of California’s available water originates in the northern one-third of the state (north of Sacramento), while more than 70 percent of the demand occurs in the southern two-thirds of the state and coastal areas. Much of the available runoff eventually flows into the Sacramento and San Joaquin Rivers, both of which flow through the Central Valley and meet in the Sacramento-San Joaquin Bay-Delta (Delta). The Delta is the heart of the state’s surface water delivery system. In any given hydrological year, the state’s water supply can be affected by circumstances from extreme drought to flooding. California’s unpredictable climate has led the state to invest in one of the most sophisticated water delivery and flood management systems in the world so this crucial resource can be made available to the communities, industries, habitats, and farms it supports.