The Massive Reservoir Behind America’s Tallest Dam Nears Full Capacity Again

California’s second-largest reservoir, Lake Oroville, reached over 99% capacity on Tuesday, May 12, with only two more feet of water needed for the lake to reach full capacity.

This month, the lake was filled 122% compared to its average fullness level during mid-May.  

This makes 2026 the fourth consecutive year that Lake Oroville has reached full or near-full capacity. 

The lake has maintained these levels for four years, two other times. These times were from 1971 to 1975 and 1995 to 1999.

In total, Lake Oroville has reached near or full capacity twelve times in the past 25 years.

The lake functions as a primary source of water for around 27 million residents in the San Joaquin Valley, San Francisco’s Bay Area, and across Southern California.

When water levels are low, millions of Californians are at great risk of losing their water supply.

This situation happened in August 2022, when Lake Oroville was only 22% full after a three-year-long drought. This was the least amount of water the reservoir had had since its 1967 construction.

When this happened, many Californians were subject to water restrictions.

Importance of snowmelt

From 2023 to 2025, Lake Oroville maintained high capacity levels due to snowmelt from consecutive wet winters.

When a state receives more rain than average during the winter, that season is referred to as a ‘wet winter.’

It is due to three straight years of wet winters that Lake Oroville was able to sustain high levels of water in 2026, despite California’s recent winter looking different. 

The state received average levels of rain during the season. Additionally, a heat wave occurred in March that melted a lot of the state’s snow.

With these factors combined, some experts have warned that California needs another wet winter, or else the lake levels may fall below average levels this upcoming fall.

A wet winter is likely also needed for Lake Oroville to maintain high levels. 

If this doesn’t occur, there may not be enough snowmelt for the reservoir to sustain high water levels in 2027.

Jeffrey Mount, a senior fellow at the Public Policy Institute of California’s water center, told Mercury News that people tend to forget about drought risks during a “wet period.”

“The candidates for governor aren’t addressing water. We’ve had three wet years and one OK year in a row. Our disaster memory half-life is very short. Whether it is a flood or a drought, we forget very quickly,” Mount told the outlet.