Hydro energy reduced as California reservoirs shrink

July 6, 2021
Jesse Vad, SJV Water reporting intern
by Jesse Vad, SJV Water reporting intern
The dam at New Spicer Meadow Reservoir in 2018. The lake should have 160,000 acre feet of water but only has 90,000 acre feet in June 2021 because of drought, which will make power generation difficult. CREDIT: Randy Bowersox, hydroelectric manager for the Northern California Power Agency
Jesse Vad, SJV Water reporting intern
Jesse Vad, SJV Water reporting intern

Share This: 

California’s reservoirs and rivers are startlingly low, forcing many of the state’s more than 270 hydropower facilities to generate less power.

Lake Oroville, one of the state’s largest reservoirs, made headlines because its water levels have dropped so low the power plant may need to shut down for the first time. While most other hydropower plants aren’t at risk of shutting down, plants that rely on watersheds up and down the state are not able to generate normal amounts of power.


The Collierville hydropower plant sits in the North Fork of the Stanislaus River Watershed. It’s the largest power plant in the watershed and combined with a few others, the plants generate 259 megawatts of energy, enough to power a quarter of a million homes. Most of the power from Collierville goes to the grid for customers near Stockton.

Collierville depends on water from New Spicer Meadow Reservoir, a 189,000-acre-foot reservoir in Tuolomne County. In June, the reservoir should have about 160,000 acre feet of water but only has 90,000 this year.

That “means we just have to be very, very selective on when we’re able to make power,” said Randy Bowersox, hydroelectric manager for the Northern California Power Agency, which operates Collierville.

He said almost all the water releases this year will be for environmental needs, such as flows for fish. Those releases will generate some incidental power, but not enough to run the plant all day as would normally be the case. Collierville will only run at times of high demand.

That puts more stress on the power grid. And with blistering temperatures slamming the San Joaquin Valley, people need all the power they can get.

The California Independent System Operator maintains the state’s power grid. Throughout June, the ISO exhorted people to conserve power, and warned there could be rolling blackouts.

For now, warnings of power shortages have been called off but hydropower operators are worried about the rest of the summer and the length of the drought.


The Pine Flat Reservoir east of Fresno, is 33% full. It should be 60% full at a minimum for this time of year, said David Merritt, interim general manager of the Kings River Conservation District, which manages the reservoir’s power plant.


Don Pedro Reservoir, east of Modesto, is also dropping due to dry conditions over the past two years, Dan Severson, assistant general manager, power supply for Turlock Irrigation District, wrote in an email. The district is making fewer water releases and generating less power, he added.


The Donnells and Beardsley reservoirs in the mountains of Tuolomne County are also unusually low. Donnells is around 80% full. But considering it usually fills every year, being this low is rare, according to Jarom Zimmerman, general manager of the Tri-Dam Project which operates the reservoirs’ respective power plants. Beardsley is a little more than half full, also rare for this time of year.

Usually, the Donnells power plant runs hard in the spring, but because there was such little runoff this year it’s hardly run at all, said Zimmerman.

“The levels don’t reflect how dire the situation is,” said Zimmerman. “We will have substantially less power generation this year compared to an average year.”

For Pacific Gas & Electric, the lack of water isn’t out of the ordinary.

“I don’t have a crystal ball,” said Paul Moreno, spokesperson for PG&E. “But we’ve certainly been through consecutive dry years before and each year we’ve used the same strategy.”

Moreno said in drought years PG&E reduces hydropower production in the spring so it can ramp up production in the summer when demand increases. Still, the company will generate significantly less hydropower this year than normal.

As of June 23, PG&E’s 16 largest reservoirs in the state are at an average of 68% of normal levels for this time of year. That includes Salt Springs Reservoir northeast of Stockton, Relief Reservoir above Stanislaus National Forest, Pinecrest Lake just west of Relief, Bass Lake northeast of Fresno and Courtright and Wishon reservoirs east of Shaver Lake.


Even with the drought, Southern California Edison will probably generate more hydropower this summer than in 2020, according to a spokesperson. That’s because the Creek Fire, which burned nearly 380,000 acres of the San Joaquin River watershed last year, forced SCE to pause generation from its Big Creek Hydroelectric Project, which includes nine power plants, until the fire passed, Gabriela Ornelas, spokesperson for SCE wrote in an email. The fire burned for nearly four months before being contained.

Some large reservoirs aren’t in such bad shape.


The New Melones Reservoir sits east of Modesto just above the valley floor. It’s operated by the Bureau of Reclamation and produces power for the Central Valley Project, the federal system of canals that bring water to agriculture throughout the valley.

New Melones can hold 2.4 million acre feet. It’s currently at 1.2 million. But that’s not an unusually low level for this time of year, said Cary Fox, hydro system controller team leader for the Bureau of Reclamation.

“Sheer size is kind of its saving grace,” said Fox. “It gives you the flexibility in how you manage it.”

This year’s water releases will decrease the reservoir’s storage because of how little refill there was. But the reservoir still has enough to last through two more years of severe drought before the powerhouse is affected, said Fox.


On July 1, the California ISO issued a call for extra power from generators throughout the west to ensure the grid will survive July and August. The ISO’s grid manager, Public Utilities Commission president and California Energy Commission chair wrote a joint statement citing the drought’s impact on hydro as one of the reasons the grid is at risk.

With so much hydropower diminished, other sources of energy have to be leaned on harder to compensate. Hydro typically makes up about 15% of California’s power generation. Natural gas usually makes up a large portion of the state’s generation, often above 40%.

While California is steadily increasing its renewable energy sources each year, a loss in hydro is still significant, said Ranjit Deshmukh, assistant professor of the environmental studies program at University of California, Santa Barbara.

“We have to be concerned about it because everytime you burn natural gas, it’s increased greenhouse gas emissions,” said Deshmukh. “And everytime we have less hydropower generation, other sources, especially historically natural gas, have taken over supplying that demand.”

Natural gas is also more expensive than hydro. And when the energy supply is strained, wholesale electricity prices increase, which means higher prices for consumers, he added.

For now, most of the power plants are surviving.

“We’ll be fine this summer,” said Bowersox. “It’s really next year that would be scary if we ended up having another dry drought year.”

Jesse Vad, SJV Water reporting intern

SJV Water is an independent, nonprofit news site dedicated to covering water in the San Joaquin Valley. Get inside access to SJV Water by becoming a member.


Receive the latest news

Subscribe To Our Weekly Newsletter & Get Email Notifications

Enter your email address to receive INSTANT ALERTS of new articles and to be added to SJV Water’s WEEKLY NEWSLETTER