After investigation, Long Lake Dam fish kill still a mystery

An investigation into what killed thousands of fish at Long Lake Dam in February ruled out some potential causes, but it was unable to definitively pinpoint the reason so many fish turned up dead.

A report from the Spokane Tribal Fisheries office found that there was no evidence the fish had been harmed by contamination from oil or gasoline, and that there were no disease or parasite levels that were out of the ordinary.

It points to gas bubbles observed on the eyes and skin of most of the dead fish as a possible culprit, but said there wasn’t enough supporting evidence to confirm that gas bubble disease was to blame.

The report represents the final word for now on the die-off at the dam west of Tumtum.

Rebecca Cook, a biologist with the Spokane Tribe and author of the report, said there’s not much more to learn about the incident, but that a task force has been set up to try to ensure a faster response the next time something similar happens.

Chris Donley, the Washington Department of Fish and Wildlife’s eastern region fish program manager, said he doesn’t expect the kill had a major impact on the fishery.

“We’ll just monitor it,” Donley said. “If they start to pop up again, we’ll dig into it a little more.”

Fisheries officials learned of the kill on Feb. 7, after a man who stopped at the dam posted a video to Facebook that showed dead fish floating belly-up.

Cook and other fisheries officials went to the dam to see what was happening. They saw a variety of species among the dead, including walleye, perch, suckers and trout. Fish of all ages were observed, the report said.

It happened a little more than a month after an oil sheen was observed on a different part of the river, which was the result of a mineral oil spill by Inland Empire Paper Co. Inland Empire Paper is owned by Cowles Co., which publishes The Spokesman-Review.

The tribe’s report says that water quality testing found no evidence that mineral oil played a role in the kill, and that levels for that and other chemicals like gasoline or diesel fuel were normal.

Another fish kill had been reported in January, and WDFW sent 20 perch carcasses off for testing for hydrocarbons, which would tell them if the fish were impacted by oil or gas. The tests didn’t detect any hydrocarbons in the fish, according to the report, and it’s unclear if the two kills are related.

After the February die-off, two batches of fish carcasses were sent to the Washington Animal Disease Diagnostic Laboratory in Pullman for necropsies. The lab analysis found some irritation and injuries in the fish, but nothing that was significant enough to explain the kill.

Cook said the gas bubbles observed on most of the dead fish, either in their eyes or their skin, represented the “best-known cause.” Fish develop bubbles when the levels of dissolved oxygen or nitrogen in water are too high for fish to absorb the gases.

Avista, which operates Long Lake Dam, installed sensors the day after the kill that measure dissolved gas. They found normal levels of dissolved oxygen and nitrogen.

Because those sensors were not in place at the time of the kill, officials don’t know if there was any change in the days leading up to the die-off.

Spilling water from a dam can affect the amount of dissolved gas in water. Above the dam, Long Lake had been rising in the days before the kill, but because there’s no stream gauge below the dam, it’s unclear if streamflow increased there.

Donley said it’s possible dam operations played a role, but that they “can’t say definitively that’s what it was.”

Jared Webley, a spokesman for Avista, said in a statement Tuesday that the company had not made any changes at the dam “that would have affected the fish or caused the fish kill to occur.”

Katelyn Scott, water protector at the Spokane Riverkeeper, said the report doesn’t eliminate the possibility of “a nefarious cause here.”

“This amount of fish kill is still concerning,” Scott said. “We still want to know what actually happened here.”