CALIFORNIA RESERVOIR REPORT

Last Updated: December 26, 2025

California's dams and reservoirs are experiencing abnormal conditions for December 2025, with many reporting historically high water levels due to a series of atmospheric river events and heavy rainfall across the state. The data indicates that storage levels are substantially above average for this time of year, with significant increases observed at major reservoirs such as Lake San Antonio, which has current storage at 270,863 acre-feet compared to its average of 132,675.92 acre-feet. Similarly, New Melones Reservoir is holding 1,983,900 acre-feet, a sizeable jump from its average of 1,443,401.24 acre-feet. Meanwhile, Lake Oroville and Shasta Dam, two of California's largest water storage facilities, lack current data, but experts are stunned by the influx, calling the rising water levels "incredible" in the context of historical trends.

The abnormal conditions are primarily attributed to persistent atmospheric rivers targeting the state, leading to severe weather warnings, significant precipitation, and flooding. This has resulted in emergency actions, such as evacuation warnings and power outages affecting tens of thousands. Additionally, the snowpack levels, a critical source of spring and summer water supply, could be affected, although specific data on snowpack conditions is not provided. The increased reservoir levels come as a stark contrast to the California Drought Summary before December 23, 2025, which classified 12% of the state as abnormally dry. Forecasts suggest continued flood threats, and Governor Newsom has declared a state of emergency to address the impact of the storms. These anomalies highlight the challenges of climate variability, with recent records set for both drought conditions and now potentially for wettest periods, underscoring the importance of adaptive water management strategies in California.

California has over 1,400 reservoirs and dams, which provide water for agriculture, industry, and households. Some of the major reservoirs in the state include Lake Oroville, Shasta Lake, and San Luis Reservoir. These reservoirs are fed by streams, rivers, and creeks such as the Feather River, Sacramento River, and San Joaquin River. The snowpack in the Sierra Nevada mountains is a crucial source of water for these reservoirs, as it melts during the spring and summer and fills the streams and rivers that flow into the reservoirs. However, drought conditions have been a major concern in recent years, with record low levels in some reservoirs. Seasonal trends show that reservoirs are typically at their lowest levels in the fall and winter, and reach their highest levels in the spring and summer. Overall, California’s reservoirs and dams play a vital role in managing the state’s water resources and ensuring a reliable water supply for its residents.

California has over 1,400 reservoirs and dams, which provide water for agriculture, industry, and households. Some of the major reservoirs in the state include Lake Oroville, Shasta Lake, and San Luis Reservoir. These reservoirs are fed by streams, rivers, and creeks such as the Feather River, Sacramento River, and San Joaquin River. The snowpack in the Sierra Nevada mountains is a crucial source of water for these reservoirs, as it melts during the spring and summer and fills the streams and rivers that flow into the reservoirs. However, drought conditions have been a major concern in recent years, with record low levels in some reservoirs. Seasonal trends show that reservoirs are typically at their lowest levels in the fall and winter, and reach their highest levels in the spring and summer. Overall, California’s reservoirs and dams play a vital role in managing the state’s water resources and ensuring a reliable water supply for its residents.