Gas trauma in fish from Libby spill
June 26, 2006
Unprecedented spill from Libby Dam has caused flood damage and increasing gas trauma symptoms in fish downstream, according to a state biologist who has been monitoring the Kootenai River.
The U.S. Army Corps of Engineers projected Thursday that releases would taper from 43,000 cubic feet per second (cfs) to 30,000 cfs by Saturday, where it would be maintained into next week. With a powerhouse capacity of 24,000 cfs, the dam has been releasing water over its spillways for the last 16 days.
Even with the spill operations, brought on by heavy rains and at least three peak inflows, Lake Koocanusa reached full pool on June 17. That led to an unprecedented spill of 31,000 cfs earlier this week, with total flows at 55,000 cfs.
The Kootenai River was running about two feet above flood stage for much of the week.
Because of the high flows in Montana, there were reports of groundwater seeping into yards and basements, docks being torn from their moorings, landscaping damage and other minor problems.
At Bonners Ferry, Idaho, there was reportedly minor flood damage at a riverside hotel, along with about $2.6 million in crop damage due to high waters seeping into fields.
Brian Marotz, fisheries projects manager for Montana Fish, Wildlife and Parks, said the spill's volume and duration is unprecedented on the Kootenai River. And it is having an increasingly adverse effect on fish, he said, because of dissolved gas accumulations that are produced by turbulence beneath the spillways.
"It will help with the spill reducing, but really it is the duration of spill that is biologically important because the symptoms in fish ramp up over time," he said.
Monitoring fish during an unplannned spill in 2002, Montana Fish, Wildlife and Parks found that gas bubble trauma in fish peaked after seven days of spill.
Using boat-mounted electrofishing gear, a state crew has been monitoring gas trauma symptoms in a three-mile reach below the dam since the spill started on June 8.
After seven days of spill, Marotz said, the incidence of gas trauma symptoms was less than what was observed in 2002, "which was kind of a surprise for us."
But after 12 days of spill, that picture changed entirely.
"By Monday, every bull trout sampled had gas bubble trauma," Marotz said. "The fish look otherwise healthy, but we're seeing bubbles in eyes, bubbles in fins and split fins."
It's believed that bubbles in the fins cause them to split.
"And as of Monday, we saw something new that we didn't see in 2002," Marotz said. "The bottom surface of the fish had little bloody pin pricks. It was very common. Nearly every bull trout had that symptom." About 80 percent of Monday's random samples of rainbow and cutthroat trout had symptoms, and about 70 percent of mountain whitefish had symptoms.
Gas concentrations, and fish with symptoms, were initially highest along the left bank of the Kootenai River directly below the spillways.
"At first the gas was hugging the left side," Marotz said. "But by Day 7 it was nearly the same on both banks and by Monday, it was almost identical on both banks."
It's believed that most fish recover from gas trauma, but it's unknown how much gas trauma they can tolerate.
"We don't know because we've never had anything like this before," Marotz said, referring to the spill volumes and duration. "We haven't found any fish that just died straight out form gas bubble trauma."
It's possible that fish are dying and sinking in the river. To check that out, there are plans to snorkel in the river, once it drops to a safer level, to look for dead fish.
"When it's safe to do so we'll swim and we'll look in places where fish would likely pile up," he said. "We're also asking people who find dead fish to let us know about them. Montana Fish, Wildlife and Parks is well aware of kokanee that have been killed or badly damaged by getting entrained in the dam's spillways."
"If they are kokanee, we have enough information," Marotz said. "But if people find dead bull trout, cutthroat or rainbow, they should call the Libby field office with locations for those fish."
There are about 400 fish that have been implanted with short-range transmitters called PIT tags. Over time, those fish could provide indications that the spill has displaced fish to lower reaches of the river, Marotz said.
So far, the electrofishing sampling has occurred in the three miles below the dam, but next week sampling will get underway much further downstream, below the town of Libby.
Gas concentrations may be less further downstream, Marotz said, but they will still exceed "gas caps" in the state's water quality standards.
"Gas saturation stays high all the way to Kootenai Falls," he said, referring to the well-known falls several miles downstream from Libby.
Reprinted from The Columbia Basin Bulletin: Weekly Fish and Wildlife News, Issue No. 356, June 23, 2006, www.cbbulletin.com
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