California's Central Valley is an agricultural powerhouse. But this agricultural abundance comes at a high cost: damage to the San Francisco Bay-Delta ecosystem. In recent decades, vast quantities of water have been diverted from the delta, the area where the Sacramento and San Joaquin rivers come together, to supply water to farms and to the state's thirsty cities, with devastating effects on fish and wildlife. Unless these diversions are reduced, the delta's water supplies -- and its incomparable natural resources -- may never recover.
NRDC analysts looked at data on water diversions from the delta by the State Water Project and the federal Central Valley Project over the last five decades, compiled into five-year averages. Averaging minimizes the effects of variations caused by changing weather conditions, making it easier to see long-term trends. The data show a steady increase in the quantity of water diverted -- coinciding with increasing damage to the delta's natural resources.
In the period 1991 to 1995, after eight consecutive periods of increase, the average dipped, to just over 4 million acre-feet diverted -- largely because of an extended drought. In the late 1990s, wetter weather returned, and pumping levels once again began to increase.
During the most recent five-year period, from 1996 to 2000, the two projects removed an average of about 5 million acre-feet per year, more than twice the amount diverted in the period 1966 to 1970. In 2000, approximately 6.3 million acre-feet were diverted from the delta, the highest level in history. Diversions by the State Water Project to fill the recently completed Diamond Valley reservoir in Southern California were a major factor in this increase.