People drawn to the beauty of Hood Canal are helping suffocate the very waters that brought them here. Septic systems leaking nitrogen from...

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People drawn to the beauty of Hood Canal are helping suffocate the very waters that brought them here.

Septic systems leaking nitrogen from sewage into the southern end of the picturesque fjord are contributing to a chain reaction that kills fish and depletes the richness of underwater life, scientists announced Monday at a summit in Bremerton.

The findings confirm what had been suspected for some time — that population growth and septic drain fields are a likely culprit behind lethally low underwater oxygen levels.

But the results of three years of intensive work by scientists have found that human impacts on an ecosystem can come even in surprising ways. Logging, for instance, has paved the way for more alder trees, which in turn release nitrogen into Hood Canal.

And it illustrates the big problems that can come when a delicate natural balance is thrown even slightly off kilter.

“It underscores that in lower Hood Canal we have a very sensitive system that has a big human component,” said Duane Fagergren of the Puget Sound Partnership, the state agency working on a plan to revive Puget Sound and Hood Canal.

The scientific findings were released at a daylong meeting in Bremerton, held nearly six years after the first in a string of fish kills set off alarms about the health of Hood Canal.

Since then, the narrow, deep canal has become a poster child for people concerned about the overall health of the Sound.

Multiple culprits

Nitrogen has long been suspected as the chief culprit for the Hood Canal’s woes, because it fertilizes algae growth. When the algae dies and decomposes, it sucks oxygen from surrounding water.

But where exactly was the nitrogen coming from? And what can make things get so bad that beaches are strewn with dead fish?

It turns out the ocean is the single biggest source of nitrogen flowing into the canal. And of the human activities, the amount of nitrogen coming from alders dwarfs septic tanks.

Low oxygen levels, meanwhile, are also influenced by weather and currents. Deep water with little oxygen can get pushed to the surface suddenly in parts of the canal when a wind from the south arrives after long periods of calm, sunny weather.

A study of layers of muck at the bottom of the canal showed low oxygen levels emerged periodically even centuries ago.

But today, heavily populated areas play a critical role by delivering doses of nitrogen during the most sensitive time, in some of the canal’s most vulnerable areas, according to researchers.

People around the southern end of Hood Canal can have a big impact during the summer when oxygen levels reach their lowest, the scientists found. And that water could be helping to feed the fish kills in the Hoodsport area.

Human influences — mostly septic tanks — can cut oxygen in the water in the southern end by half, or more, during critical summer months.

Harmful oxygen levels

For fish, that can make the difference between life and death.

Jan Newton, the University of Washington scientist leading the research effort, noted a state Fish and Wildlife Department study that found when oxygen levels fall below 2 milligrams in a liter of water, rockfish start moving to avoid the water.

When it falls below 0.7 milligrams, it can kill the fish. Humans can cause as much as a 1 milligram drop in the lower Hood Canal during the summer, the scientists found.

“If you’re in a low oxygen year and you add humans, that could kill fish,” Newton said.

In addition to fish kills, there are fears that chronically low oxygen is causing other damage.

Fishermen are facing a steep drop in their catches, which some suspect is tied to lower oxygen levels.

The catch for tribal and nontribal fishermen has fallen from nearly 700,000 pounds in 2000 to 268,500 in 2007 and 2008.

A white bacterial mat periodically forms near the canal’s southern tip and covers as much as 8 square kilometers.

U.S. Rep. Norm Dicks, who has helped steer more than $7 million in federal money toward the research, said remedies will likely include costly new sewage systems for parts of Hood Canal.

“I think we’re going to find that we have to put sewer systems in the lower Hood Canal. It’s going to be expensive,” he told people gathered in Bremerton. “Now, I don’t have any magical way to fund this.”

The Belfair area is already planning to build a $25 million sewage plant, expected to open in 2011.

Three other communities in the southern part of Hood Canal are planning sewage plants as well.

Meanwhile, a nonprofit banking program, ShoreBank Enterprise Cascadia, has loaned money to replace 66 septic systems in the three counties surrounding Hood Canal. It’s estimated there are as many as 25,000 septic systems surrounding the canal.

Warren Cornwall: 206-464-2311 or