Who Has the Power?

Operational & Mission Changes Impact Dams’ Power Output

Story and photos by Rural Montana Editor Ryan Hall

The 4 lower Snake River dams have long been an important source of power for the Pacific Northwest. But the amount of power they produce during the 9 months each year that fish pass through the dams has been reduced, and that impacts electric cooperatives in the Northwest.

The lower Snake River dams are Ice Harbor, Lower Monumental, Little Goose, and Lower Granite dams. Each 1 has 6 turbines. Combined, the 4 dams can produce enough electricity to power all of Montana and Wyoming, according to Paul Ocker, chief of operations and maintenance for the Walla Walla District of the Army Corps of Engineers, which manages the dams.

Ocker said the mission of the dams has changed since they were built in the 1960s and ’70s.

“The main reason they were built was for navigation,” he said, noting hydropower was later added to the dams.

Staff at Lower Granite and Ice Harbor dams said all 4 dams were built with fish ladders for returning adult fish. Additional fish-passage measures for juvenile fish were added later.

In Ocker’s 24 years with the Corps of Engineers, he says has seen power take a backseat to fish considerations.

“The focus is even greater on fish than when I first got here,” he said. “For the Snake River dams, I think we are reaching the limit of what we can do.”

In 2022, the 4 lower Snake River dams produced 6.6 million megawatt hours of power, or enough to provide electricity for about 600,000 homes. That’s a lot of power, but it’s a lot less than it used to be—and could still be.

be—and could still be. “In the last 25 years, we are producing a lot less power than we used to,” Ocker said. “We are spilling a lot of water for fish migration—a lot more than we used to.”

He explained that in the past, each of the 4 dams on the lower Snake River typically ran 5 turbines. This spring, with low flows a new court settlement, and biological opinion dictating spillage, the dams typically ran 1 turbine, often at minimum generation.

“We don’t make a decision without considering fish,” said Brian Vorheis, operation project manager for Ice Harbor Dam.

Rob Lustig, operation project manager at Lower Granite Dam, said that’s the case there as well.

“A lot of things we are doing differently are related to that biological opinion,” Lustig said. “Here, hydro is not king.”

For example, on May 23, Ice Harbor Dam spilled 69,000 cubic feet per second of water through its spillways. Think of each cubic foot as being about the size of a basketball. Just under 10,000 cfs of that water was used to generate what dam officials call “min-gen,” or minimum generation—about 75 megawatts. That means roughly 7 times the amount of water being used for a generation was spilled to aid juvenile fish migration.

A day earlier, Lower Granite had 1 turbine running at min-gen, producing 85 MW. Turbines at Ice Harbor can produce a maximum between 102 MW and 111 MW each, while Lower Granite turbines each produce up to 135 MW.

Normally this time of year, 3 to 6 turbines were running at up to max output, Lustig said.

“How much we generate right now is dictated by a settlement agreement that is overseen by the courts,” Ocker said. “It is the desire of the environmental groups and the plaintiffs to have all fish pass by a non-powerhouse route.”

He said typically the fish survival rate through a turbine is about 90%, while it’s 98% through other passage routes, such as the spillway or when diverted around the turbines by fish screens.

Ocker noted the new turbines at Ice Harbor have a fish survival rate between 96% and 98%.

Before the settlement agreement, a biological opinion issued by the National Oceanic and Atmospheric Administration dictated how much energy the dams could generate.

“We spilled excess water if there was not enough demand,” Ocker said. “Now we spill specifically for fish 8 or 9 months out of the year. As the Corps of Engineers, what we are required to do is balance what the people need and what the environment needs.”

Vorheis said that once Ice Harbor reaches the 10,000 cfs inflow it needs to run 1 turbine at min-gen, it must spill the next 110,000 cfs to meet the current operating plan under the settlement before it can generate more power. Vorheis said that without a mandated spill, 96,000 cfs would be enough to generate at maximum power. The plan requirements mean it now takes a river flow of 206,000 cfs to run all 6 turbines at maximum output.

“I don’t know if we will ever see all 6 lights on again,” Vorheis said, referring to the lights on the turbines that show they are running. “4 years ago, we were running all 6 units. Since spill kicked off in April (2024), we’ve been running 1 unit at min-gen.”

Brad Sharp, chief of operations at Lower Granite Lock and Dam, said that since 2020, the total project generation has decreased between 20% to 25%, with most of that coming in the spring salmon run of April until mid-June.

That generation is variable based on snowpack each year, but the 5-year averages show a trend. From 2015 to 2019, Lower Granite Dam produced an average of 307,930 megawatt-hours in April. From 2020-2024, the 5-year average for April was 91,224 MWh. For May, the average dropped from 385,103 MWh to 202,691 MWh over the same time frame.

1 key element that remains—even with the fish passage plan, biological opinions, and court settlement—is that hydropower stands at the ready in case of a power emergency where demand outpaces supply.

“There’s still the availability component,” said Harold Wentworth, chief of operations for Ice Harbor. “That availability is still important to the reliability of the grid. If an emergency were to happen, we would deviate from the fish passage plan with appropriate coordination.”

He said if the Bonneville Power Administration called for more power— which happens if intermittent generators such as wind or solar stop producing— backup power must already be spinning.

“In this region, that is primarily hydropower,” Wentworth said. Ice Harbor Dam can produce an additional 100 MW in 2 to 3 minutes and can be at full power within 8 minutes, Wentworth said. The same is true up and down the Snake River, including at Lower Granite Dam.

“In 6 minutes, we can go from not generating anything to powering a city the size of Portland,” Lustig said.