WHAT’S GOOD FOR RENTON isn’t necessarily good for salmon. Next week long-overdue dredging will begin in the Cedar River near the mouth of Lake Washington. This $8.5 million project will help control a growing flood threat to downtown Renton—but also create new problems for the Cedar’s fragile sockeye and chinook runs.

On June 16, work crews will begin removing tons of sediment and gravel from the last 1.25 miles of the river, lowering its bed by 4 feet. This, along with new levees and flood walls, will prevent floodwaters from overtopping the river bank and inundating the nearby Boeing plant, municipal airport, and downtown district. And it will complete a drastic alteration of the Cedar’s course that began around 1912. The river originally flowed past Lake Washington into the Green River. But Army Corps of Engineers spokesperson Mary Martz says sharp-eyed Seattle investors, hoping to build a freshwater port, finagled an artificial channel through their Lake Washington property. The port never materialized, but the altered river remains.

Unlike a naturally sloping riverbed, the artificial waterway is flat and prone to sediment build-up. Until 1982, says Martz, the lower Cedar was periodically dredged. Since then, the channel has become choked with dirt and gravel. The Army Corps says the river is certain to overtop its banks in a future flood.

All this would cause considerable pain to Boeing, whose 16,000 workers turn out $14 billion worth of airplanes a year. “They’re trying to get out a plane a day,” says fisheries biologist Eric Warner, who’s followed the project for the Muckleshoot Indian tribe. “They make ’em on one side of the river and fly ’em out on another. [If it floods] they just stack up.” And so King County, Renton, and Boeing are each pitching in $1 million for the project, while the corps picks up the rest. County Council member Rob McKenna, whose district includes parts of Renton, sees “no other option [than dredging].”

McKenna argues that the project will also benefit sockeye salmon that spawn in the flood-prone lower channel. But the Muckleshoot tribe has appealed the state’s fisheries permit, claiming that the flood control project does more harm to the salmon than good. “We’re not so concerned about the actual dredging,” says Eric Warner. “The mitigation is grossly inadequate.”

DREDGING MAY REDUCE sockeye spawning, which has increased in the lower channel in the last two years. More importantly, though, it will likely benefit predators that dine on juvenile salmon. Scientists suspect that trout, sculpin, and squawfish have contributed to the decline in Cedar River chinook and sockeye in recent years (though sockeye have bounced back somewhat). Because the river channel was dug lower than Lake Washington, lake water backs up into the Cedar, slowing its flow and the baby salmon’s exit. “Where the water slows down it’s easy pickings,” says Warner. Dredging will boost the backwater effect. That means more baby sockeye and chinook (an endangered species candidate) on the lake fish’s menu.

The Army Corps of Engineers acknowledges that dredging will affect sockeye and chinook and has earmarked $850,000 for mitigation, including revegetation of the riverbanks and delta, construction of a sockeye spawning channel in the lower Cedar, and additional chinook and coho habitat enhancement further upriver. The idea is to augment spawning and habitat upstream to balance increased losses to predators downstream. “It’s a good start,” acknowledges Eric Warner, “but it only covers a small percentage of the impacts.” He points out that while more than a mile of river habitat will be dredged, only 700 feet of chinook habitat will be created in the lower stretch of the river. Even as the dredging start looms, the Muckleshoots have asked the state Department of Fish and Wildlife to require additional salmon-enhancing measures.

Council member McKenna doubts that additional mitigation funding is available and, with predation solutions so uncertain, that fisheries scientists could use it effectively anyway. For now, the Army Corps is on wait-and-see mode, pending post-construction monitoring. “We’ll know more as we go along,” says Martz. Should the monitoring data call for it, the project plan includes contingencies for more mitigation.

But the Muckleshoot appeal raises a nagging question: More habitat enhancement can clearly be done on the Cedar. Why go for the minimum? King County positions itself as a leader in saving salmon. Shouldn’t that include going the extra river mile?