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Gigantic Fish Kill: State Confronts a New Threat in Gas-Charged Water Blamed for Nimbus Fingerling Deaths

Posted on: Sunday, 21 May 2006, 12:00 CDT

By Edie Lau, The Sacramento Bee, Calif.

May 21--California, often a leader in setting environmental standards, has none for a water-quality problem that is contributing to the fish killed at Nimbus Hatchery.

The problem, known as dissolved gas supersaturation, causes gas-bubble disease in fish. Divers experience a similar sickness known as "the bends."

Gas supersaturation has been the subject of numerous workshops and studies in the Pacific Northwest for decades. At least 20 years ago, the U.S. Environmental Protection Agency recommended states set limits on dissolved gases in waterways.

But the issue is new to California, coming to the fore only since workers at Nimbus Hatchery began in the past week to remove dead salmon by the tens of thousands a day from their concrete troughs on the American River.

Jim Canaday, a senior environmental scientist at the state Water Resources Control Board, said that up to now, "It hasn't been a problem. ... It's something we'll have to look into," he added.

The hatchery fish, fingerling salmon that during a normal spring would be planted in the Bay Area to mature in the ocean, are suffering from a mix of woes.

Two are infections: One, called coldwater disease, can be treated with antibiotics. The other, infectious hematopoietic necrosis, is a viral infection for which there is no treatment.

The third is gas bubble disease, which can kill or stress fish, making them more vulnerable to other illnesses.

About 1.2 million out of 5.1 million Nimbus salmon have died in the past month. The hatchery was established to produce 4 million salmon annually to compensate for a loss of spawning habitat due to the construction of Nimbus and Folsom dams 50 years ago.

State Department of Fish and Game officials attribute the gas-bubble disease to frequent and prolonged periods of exceedingly high runoff last winter and this spring, caused by abundant rainfall and snowmelt. Massive volumes of water have been coming out of the Folsom and Nimbus dams off and on since Christmas.

The gas-bubble problem results when water plunges -- whether over a natural drop or a dam -- into receiving waters with great force. The turbulence forces excess air into the water.

Under this condition, known as supersaturation, atmospheric gases dissolve into liquid. Eventually, the gases come back out, bubbling to the surface and returning to the atmosphere.

It's like soda pop: Carbon dioxide gas is driven under pressure into liquid. Opening the container relieves the pressure, allowing the carbon dioxide to escape as fizz.

Breathing supersaturated water is bad for fish because the excess air forms bubbles in their bodies. The bubbles can block blood flow and kill tissues. An obvious symptom of gas-bubble disease is known as "pop eyes."

At normal pressures, water is 100 percent saturated with atmospheric gases, principally nitrogen and oxygen. Since at least 1986, the U.S. EPA has recommended that states limit total dissolved gas concentrations in waterways to 110 percent.

At Nimbus Hatchery, readings taken over the past seven weeks show dissolved gas levels as high as 175 percent, with a recent decline to as low as 128 percent, hatchery manager Terrance West said.

The higher measurement -- 175 percent -- is virtually unheard of, and even the lowest reading is high. John Beeman, a U.S. Geological Survey biologist who has studied gas-bubble disease in fish on the Columbia River in Washington, said researchers typically study levels of 130 percent or below.

There's no point in examining higher concentrations, Beeman said. "It's like traveling at 10 times the speed of light -- we don't do that very often, so we don't worry about it too much."

So astronomical are the Nimbus readings that William Cox, a senior fish pathologist at the California Department of Fish and Game, doesn't trust them.

"When I was told of those readings, the first thing I said was, 'It's a miracle there's a live fish there,' " Cox said.

The trouble is, the measurements were taken with a new meter, and are the only readings the hatchery has. Neither the Department of Fish and Game nor the U.S. Bureau of Reclamation, which operates Folsom and Nimbus dams, regularly monitors gas supersaturation.

State fish pathologists are more focused on tracking down the virus that causes infectious hematopoetic necrosis, because even without the stress caused by gas supersaturation, the virus can be devastating to salmon.

Moreover, heavy spilling from the dams happens only intermittently, said Armando Quinones, a senior hatchery supervisor.

Still, other hatcheries in Northern California have installed equipment that routinely aerates the water -- adding oxygen or releasing excess gases as needed.

In Washington and Oregon, grappling with dissolved gas supersaturation is something of a mini-industry.

Many dam operators have installed expensive flow deflectors that cause water to spray out laterally rather than plunge down, blunting the force that drives excess gas into the water, said Blaine Ebberts, a fish biologist in Portland with the U.S. Army Corps of Engineers.

One reason those states have a bigger problem with supersaturation is that many dams spill water regularly as a way to help salmon above the dams move downstream, Ebberts said.

In the American River, salmon are not allowed to move past the dams in either direction.

Also in Oregon and Washington, salmon move upstream and downstream through most of the year.

Canaday, the California Water Resources Board environmental scientist, said fish swimming upstream to spawn during spring runoff would encounter a potentially deadly problem if they tried to pass a dam spilling supersaturated water.

That doesn't happen in Sacramento because the salmon runs preserved on the American River are fall-run chinook.

However, if climate change causes more episodes of extreme weather that result in more-frequent high-water years, Canaday acknowledged, supersaturation of rivers could become a more familiar problem in California.

"I know a lot of the planners in the state agencies are looking out 20, 30, 50 years (into the future)," he said. "Here's another one we need to add to the list."

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Source: The Sacramento Bee

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