Zach Frankel held out an oil-drowned moth, his hands browned and slippery with crude oil. He had plucked the insect from a small eddy in a shady gulch on Red Butte Creek, where 33,000 gallons of oil from a leaking pipeline had run a week earlier.

Chevron planned Saturday to wash away some of this residual oil by flushing the creek Saturday afternoon with water from Red Butte Dam. Absorbent boom was laid on the water to grab the lingering particles, and tankers waited at Liberty Park downstream to suck up oil that pooled in the pond.

But Frankel was skeptical that the flush would prove as effective at cleaning as it would spreading the oil over the stream banks once more.

"Ugh," he said, prodding the dead moth over the oil on his fingers. "How are you going to get rid of that?"

It's a question being asked by Chevron, the government agencies overseeing its cleanup, environmental activists like Frankel and thousands of people concerned about spill-impacted waterways.

"How clean is clean?" Frankel mused, echoing the question posed last week by a Chevron spokesman. "That's a good question."

The answer, it appears, is too complicated to offer now. While the ducks and geese have had their feathers scrubbed clean from the Red Butte Creek oil, the toll on vital but less photogenic species, like the moth or river algae, is much harder to grasp.

Marine biologist Riki Ott understands what Salt Lake City is going through. Her life changed forever after the Exxon Valdez tanker dumped 11 million gallons of crude into the waters outside her Alaska home.

"The thing we learned from the Exxon Valdez is that oil does cause lingering harm," she said.

Oil seeped into beach sediment and cleanup with hot-water pressure washing later killed the tiny plants and animals on the bottom of the food chain. It wiped out a generation of herring and fatally fouled the egg nests of salmon, she pointed out.

"You can't breathe an all clear," she said, "for a couple of generations."

John Isanhart, an ecologist for the U.S. Fish and Wildlife Service, said migratory birds, endangered species and the habitats that support them are focuses of the cleanup for his agency. Together with other state and federal agencies developing cleanup, restoration and monitoring plans, the Fish and Wildlife Service will weigh the various risks posed by the oil against the various methods for removing it all from the environment.

"Right now, our goal is to get rid of the risk to the public and the environment,"Isanhart said. "Sometimes, it's a long-term process that takes years. In this case, it's not going to take that long."

Government agencies overseeing the cleanup might possibly conclude that it would be better to leave behind small amounts of contaminants -- levels that studies suggest are "acceptable" -- than to destroy important habitat in the effort to get at every droplet of oil. On the other hand, findings could suggest it would be a hazard not to dig it all up.

"It gets complicated," he said.

Walt Baker, director of the Utah Division of Water Quality, said data being collected now will be key in determining when clean is clean. Post-spill information about air quality, water contaminants and other environmental factors need to be compared to prespill conditions, he said.

"Certainly, it could disrupt the food web," Baker said of the crude oil. "The product could have some long-term consequences for the sediment."

It already appears to be having some unusual impacts on the water.

Chemical loading in Red Butte Creek and the Jordan River has starved the waterways of essential oxygen in some places. Only more testing and monitoring will tell the best way to deal with that problem, which could harm the carp, catfish and other aquatic life in the river, Baker said.

Chevron spokesman Dan Johnson notes that a few factors are likely to facilitate the company's goal to "restore" the affected areas. They include the short period the oil has had to soak into the soil and the urban character of the creek and the river.

"It's going to be a lot of hand cleaning." Johnson said, noting that digging, replanting, brush-scrubbing rocks and pressure washing will be the most-used tools. "It's going to be a lot of hard work."

In the end, environmental regulators at the U.S. Environmental Protection Agency and in Utah's Water Quality Division will have to sign off on both the cleanup and future monitoring.

Peter Hayes, a biology teacher who lives along Red Butte Creek, still worries about the tall trees that shade the back of his house and shelter the snippet of chortling stream that runs through his backyard. He's worried about more oil slathering its banks, about oil choking the fine roots that nourish the trees and plants.

"Clean will not be what the EPA says," Hayes asserted. "Clean will not be what Chevron says. Clean will be what we the people of the creek say."