After years of heated debates and delays, the world’s largest dam removal is currently underway on the Klamath River across the California-Oregon border.
Established in the early to mid-1900s by energy company PacifiCorp, the four dams have stored water and generated electricity for the region. But they’ve also prevented endangered salmon from reaching critical habitat and breeding grounds, contributing to a 90 percent decrease in some populations over the last century.
Experts say that lowering these dams will help struggling salmon populations bounce back and revitalize the river ecosystem. However, removing structures of this size come with negative side effects—from droves of dead fish to muddy waters.
As a result, critics have recently spoken out against the project, deeming it an “environmental disaster.” But scientists say that they expected many of these short-term impacts before the effort began and they will soon fade. For today’s newsletter, I decided to dig into the science behind dam removal, and how the rocky start to the Klamath River project could yield a healthier river system overall.
Restarting the flow: When a dam is installed, it interrupts the natural flow of a river, which can change many of the dynamics in the ecosystem, including its temperature, biodiversity and chemical composition.
“It’s a lot like what would happen if you put a tourniquet on a part of your body,” Ann Willis, the California regional director at the nonprofit American Rivers, which has supported Klamath dam removal efforts, told me. “You can’t block a river’s flow and expect it to have no impact on any of the other living systems that are responding and interacting with that flow.”
In the Klamath River, harmful algal blooms and parasites often thrived in the stagnant reservoirs behind the dams due to their warm temperatures and lack of flow, reported Scientific American in 2020. Additionally, over time, sediment that would have flushed through the river instead accumulated in the reservoirs of these four large dams over the last 60 to 100 years.
“Sediment accumulates in the reservoir and downstream, below the dam, is sediment-deprived,” Leroy Poff, a riverine ecologist at Colorado State University, told me. He added that when too much sediment accumulates in a reservoir, it reduces that amount of water that the system can hold, which can lead to overflow and flooding.
But all that changed this winter, when several artificial reservoirs in the Klamath were emptied and the Iron Gate dam, the smallest of four dams slated for removal, was lowered.
Dam Removal: Along with restoring part of the river’s flow, this effort dumped an estimated 2.3 million tons of sediment into the system, turning the clear water into coffee-colored muck, reports the Los Angeles Times.
On March 27, Siskiyou County in Northern California proclaimed a local emergency due to poor water quality concerns related to the sediment, and others have noted an increase in dead fish or animals like deer and beavers caught in the mud around the banks. But officials say that this is a necessary step for the river to flush the sediment.
“The river is undoing a century of being impacted by these dams, and that may look messy right now,” Shari Witmore, a fisheries biologist in NOAA Fisheries’ Klamath Branch, said in a statement. “It’s moving all that sediment faster and more efficiently than we ever could, so what we are seeing is a very good thing.”
But sometimes the negative impacts of dam removal aren’t entirely expected. On Feb. 26, the California Department of Fish and Wildlife released 830,000 Chinook salmon hatchlings upstream of the dam to continue building back populations. But a few days later, many of these tiny fish washed up dead downriver after passing through the 9-foot-wide tunnel in the dam removal site, reports Cal Matters.
Officials believe the salmon suffered from “gas bubble disease”—similar to decompression sickness in scuba divers—due to the high pressure of the water now flowing in the area.
“One could argue that this was an ill-timed release, they should have thought about what was going to happen,” Poff said. Following this event, officials have stated that they will not release any more hatchlings upstream of operations until the removal is complete.
Learning by Doing: Similar negative side effects occurred during two large dam removals in the Elwha River in Washington between 2011 and 2014, which released 20 million tons of sediment downstream overall.
More than a decade later, this river has radically transformed, seeing a rise in salmon, summer steelhead and Pacific lamprey populations—enough for a tribal fishery to open last October, reports KNKX, an NPR station in Washington.
However, the Elwha is closer to the ocean than the Klamath, which has had a longer stretch of river affected by the dams. While past studies have found that rivers start returning to pre-dam conditions within two years of removal, the Klamath project is the biggest removal to date, so it’s difficult to say when negative impacts will fully subside, said Poff.
“You really have to sort of adopt a longer term point of view when you think about the river recovery,” he said. “But the river will heal. And hopefully, naturally reproducing populations of salmon will proliferate.”
And as dam removal continues, Indigenous tribes are leading a simultaneous effort along the riverbanks to plant millions of seeds to bring back native vegetation such as white oak acorns, and experts expect decades of restoration work ahead.
“It’s a beautiful thing, and a beautiful feeling, that that process of healing has begun,” Leaf Hillman, a member of the Karuk Tribe who spent more than two decades campaigning for the removal of dams, told the Los Angeles Times.
More Top Climate News
Although some countries made strides last year in reducing deforestation—including Brazil and Colombia—a new report found that the world lost 9.1 million acres of primary tropical forest in 2023.
The good news is that this is about 9 percent less than the year before. But the bad news is that destructive fires in Canada and agriculturally-driven deforestation in other parts of the world have hindered countries’ progress toward the global goal of stopping all forest loss by 2030, reports The New York Times.
“Global leaders sent an undeniable message that forests are critical to meeting global climate goals,” Rod Taylor, the global director for forests at the World Resources Institute, which authored the report, told the Times. But, he also said that “we are far off track and trending in the wrong direction.”
Meanwhile, meteorologists are forecasting a potentially catastrophic Atlantic hurricane season starting in June. A forecast from Colorado State University suggests that there could be as many as 23 named storms in all, with 11 hurricanes—more predicted than ever before, writes CNN. Experts say that coastal residents across the U.S. should prepare for this by updating their emergency first aid and storm kits, and remaining aware of evacuation routes in their area.
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