Drawdown results in thousands of dead fish

By Sarah Brown
Of The New Era/Lebanon Local

Thousands of dead juvenile fish started showing up below Green Peter Dam this weekend, causing concern among recreationists who saw the carcasses floating downstream and gathering in clumps along shorelines.
Reed Fischer, STEP biologist with Oregon Department of Fish and Wildlife, said the fish were Kokanee salmon that, according to a pathology report, died as a result of barotrauma. Known as decompression sickness or “the bends” in humans, barotrauma is a deadly experience that happens from a rapid change in depth and oversaturation of gas in the blood.

Recreationists set out for a day on the river at Sunnyside Park on Oct. 8. Photo by Sarah Brown

“It looks like that’s what happened to these fish here,” Fischer said. “They had an oversaturation of nitrogen and other blood gasses, and that causes barotrauma, or gas bubble disease. It puts bubbles in their bloodstream and their body cavity.”
The barotrauma was caused by a deep drawdown of Green Peter dam, which is a new action by the U.S. Army Corps of Engineers stemming from a lawsuit to protect Chinook salmon, a species that is listed by the Endangered Species Act. A 2021 injunction issued by Federal Judge Marco Hernandez requires Green Peter be drawn down to some 142 feet below minimum conservation pool by fall in an attempt to help the juvenile Chinook pass through the regulating outlet (RO). The RO is situated low on the dam.

To do that, the Corps started drawing down water in late summer, and Fischer said the Kokanee were probably near the RO this weekend, which is why they are now getting pulled through and being affected by the pressure changes.
“This would be a total dissolved gas issue, for sure,” he said. “When the water spills from the dam at a great height, it mixes in a lot of gasses on its way down, so it creates this super bubbly, oversaturated water on the bottom; it’s rough on fish.”
Fischer joined a team on Friday to study the fish and concluded an estimated 4,500 carcasses were observed that day. They also studied the water and found it to be normal and as expected at 58 to 62 degrees.

Dead fish gather in a clump near the boat ramp at Sunnyside Park on Oct. 8. Photo by Sarah Brown

“A certain number of fish deaths are to be expected whenever you change the water level,” he said. “But 4,500, just visually it’s a lot of fish. It looks bad. It’s very sad.”
By the time the targeted species, Chinook salmon, reaches the RO, they will not be as affected by barotrauma because the head pressure will be less, said Greg Taylor, supervisory fisheries biologist for the USACE Willamette Project.
“We’re trying to create a scenario where there will be good passage conditions for Chinook,” Taylor said. “In getting there, because the Kokanee are where they are in the water column, unfortunately they (the Kokanee) are being pulled in right now.”
According to Taylor, Chinook were placed in Green Peter in the early years of the dam, which was built in the mid-1960s, but the designed downstream fish passage didn’t work, so it was “mothballed.” As a result, there were basically more hatchery Chinook produced in mitigation. That is, until last year.
“Just last fall, Chinook were put up there to spawn, so that’s the group of fish that’s in the reservoir available to pass right now from the previous fall spawning,” he said. “But this is a different scenario with the Endangered Species Act in trying to reestablish some of these populations above the dams.”
The injunction ultimately required the Corps to assist Chinook passage downstream through the regulating outlet.
“If there was a safe passage route closer (to the top of the dam), we wouldn’t need to do the drawdown,” Taylor said. “The depth of the drawdown is driven entirely by the depth of that potentially safer route through the regulating outlet. If the regulating outlet was much shallower, that’s where we’d be targeting; but, unfortunately, the regulating outlet is quite deep, and that’s what’s driving the depth of that drawdown.”
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A researcher for EAS counts fish carcasses at the Green Peter tailrace on Oct. 8. Photo by Sarah Brown

Researchers at Environmental Assessment Services have been studying the number of fish passing through spillways, powerhouse outlets and regulatory outlets at the Green Peter head and tailrace since March 2022 by using rotary screw traps.
“We’re doing work that’s part of that injunction order,” said Dillon Alegre of the EAS. “We’re just doing downstream volitional fish passage monitoring, specifically for spring Chinook salmon. We’re there to see how the juveniles are doing coming out of Green Peter reservoir through the dam.”
More information and results of the studies can be found at https://www.nwp.usace.army.mil/Locations/Willamette-Valley/Injunction/.

A fish found at Lewis Creek Park on Oct. 8 swims in circles on its back toward the shoreline. Photo by Sarah Brown

Agencies involved in the operation wanted to remind dog owners to be vigilant about keeping their dogs away from dead salmon. Salmon carcasses may harbor bacteria in their blood called Neorickettsia helminthoeca that can make dogs very sick. Without treatment, salmon poisoning is often fatal. Symptoms include severe vomiting and diarrhea. With treatment, most dogs will survive. If a dog is seen eating a dead salmon, or even around one, take them to the veterinarian right away. Don’t wait for the dog to get sick, as prophylactic treatments can prevent a more serious illness. The sooner a dog gets treated, the less likely they will get sick and need expensive treatments.

The City of Sweet Home announced on its Facebook page that, despite the alarming number of dead fish, the city drinking water is still safe. The city’s water supply is drawn at the Foster dam. The statement read, “We are constantly testing the water at our treatment facility and have noticed no change in turbidity or quality. Sweet Home’s drinking water is still safe to drink and use as normal.”