Written by by Kiley Price at insideclimatenews.org
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.”