Pointing to this year's record-low steelhead run, some Columbia Basin fish managers are asking BPA and the U.S. Army Corps of Engineers to wait until December before using an operation that stops the flow at lower Snake River projects during the night—holding back the river for up to six hours so the water can be used to generate power during the day, when demand and prices are higher.

A provision in the Columbia River System Operations 2020 record of decision and BiOp allows the federal agencies to use the so-called zero nighttime flow operations on the Snake River beginning Oct. 15 instead of starting on a date after Dec. 1 when few fish are migrating through the system.

Corps and BPA representatives on the Columbia River Technical Management Team said they were not prepared to vote on the system operational request (SOR) at the Sept. 15 meeting, so the issue was delayed to Sept. 22.

Zero nighttime flow operations have been used for the past 16 years at the four lower Snake River dams. But fish managers from Washington, Oregon and several tribes say stopping the river's flow may impede or delay fish migration, and does not support normal ecological river functions.

Until last year, guidelines required the federal agencies to wait until at least Dec. 1 and use a sliding scale to evaluate when there are "few, if any, actively migrating anadromous fish present in the Snake River." The start date was previously based on the number of adult steelhead at Lower Granite Dam compared to the run size.

Jay Hesse, TMT member representing the Nez Perce Tribe, noted that with a steelhead run of fewer than 30,000 fish, their request would put the threshold for starting zero-flow operations after Dec. 1, as soon as there are 10 fish or fewer at Lower Granite Dam.

He said the BiOp's new allowance to start 45 days earlier—on Oct. 15—means that zero-flow operations can occur when juvenile fall Chinook and adult fall Chinook, coho and steelhead are all actively moving through the system.

"That zero-flow operation changes the once-riverine environment that's now a reservoir into a lake," he said. Without flow through the turbines, or as spill, there's no downstream passage opportunity for juvenile salmon, he noted. And although flows through fish ladder operations are maintained, they are likely ineffective at attracting adults, he added.

TMT fish managers last year made a similar request to delay the operation until after Dec. 1, but federal agencies said they could not implement it because it was outside the scope of the newly adopted CRSO BiOp. Fish managers were especially concerned about the impact to adult fall Chinook and adult coho, which are still migrating through the lower Snake River dams on Oct. 15 and have minimal time before they need to arrive at their natal streams to spawn.

"Many of these adults move through the Lower Snake in ripe spawning condition, with spawning typically starting in early-October and extending into early-December," the 2020 SOR states.

Fall Chinook passing Lower Granite Dam peak in late September and continue through late November. Coho migration through the Snake River starts in mid-September and continues through late November, their request says. The operation may directly impact the 5 to 9 percent of steelhead that pass Lower Granite Dam at night, it said.

The issue went to the Regional Implementation and Oversight Group, an interagency group that makes high-level policy decisions on Columbia River operations, but there were no changes in the Corps' and BPA's position.

This year's request came from the states of Oregon and Washington, the Nez Perce Tribe, Yakama Nation, Warm Springs Tribe, Spokane Tribe of Indians and the Confederated Tribes of the Umatilla Indian Reservation.

The fish managers said they were disappointed they hadn't seen a full evaluation of the impact of last year's expanded zero-flow operation. In January, BPA presented initial findings of a study done through a contract with the University of Washington to evaluate impacts of the operation, but it hasn't been finalized or released.

Erick Van Dyke, who represents Oregon on the TMT, said he is not supportive of turning run-of-river operations into storage dams, and added that it would be helpful to know what was done and what is being done to evaluate the operation.

Charles Morrill, a TMT member representing Washington, said fish managers had no new information available to help them understand the impacts of last year's change. "We would err on the side of conservation," he said.

Fish managers also noted that the impact of a zero-flow operation on juvenile fall Chinook is unknown. TMT members said that during zero-flow operations, water flowing through the juvenile bypass system is significantly reduced when there's no water going through turbines.

Claire McGrath, representing NOAA Fisheries, said that based on less-than-perfect information, her agency considered the data on salmon and steelhead timing of presence, behavior and passage timing in the 2020 BiOp. The agency—which did not sign onto the SOR—determined there could be impacts to some individual fish under the expanded operation, but there were not likely significant differences, she said. She said some of the data considered showed fewer than 10 percent of adult fall Chinook and fewer than 20 percent of adult steelhead migrating through the Snake River dams after Oct. 15. Additionally, most adults migrate during the day, so a zero-flow operation at night impacts fewer fish.

McGrath said under the operation, migration of adult salmon may be delayed for hours, or days, but steelhead move around a lot in the system over the winter, so would likely be less affected compared to adult fall Chinook.

"NOAA definitely appreciates our co-managers' perspective that stopping river flow, even for a limited number of hours, is objectionable, and it is not the preferred condition of the river system," she said. She said NOAA Fisheries evaluates any operation in terms of the potential benefit or potential harm to fish, and this operation is the same. If there's new information, she said, NOAA Fisheries is very interested in discussing it.

Prior to the TMT meeting, the Fish Passage Center provided a memo with a summary of last year's zero-flow operations that did not evaluate impacts to fish, but looked at how often BPA used the operation. It noted that from Oct. 15 through Feb. 28, there was no flow through one of the four dams for a total of 938 hours—about 7 percent of all hours or almost 20 percent of the hours when zero-flow operations were allowed. Of those, 291 hours were used before Dec. 5, when zero flow would have been allowed prior to the new BiOp. That also represented about 20 percent of the total hours when zero-flow operations were allowed.

The BiOp also allows for zero-flow operations for up to three daytime hours each day from Dec. 15 through Feb. 28, but only six total hours of zero-flow operations were used during that period, the Fish Passage Center reported.

Nez Perce Tribe's Hesse noted that during the newly allowed period of time, zero-flow operations occurred at each of the dams between 10 and 19 times before Dec. 4; each dam recorded between 41 and 88 hours of zero-flow operations; and the operation was implemented on consecutive nights between three to five times at each of the four dams.

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K.C. Mehaffey covers fish issues for Clearing Up, and is editor of the NW Fishletter. She joined the NewsData writing team in February 2018. From lawsuits to scientific studies, she is enjoying the deep dive into the Columbia Basin's many fish topics.