The incident command team also said:
• Less diesel has been recovered than estimated. The new estimate nearly 15,000 gallons is roughly one-third less than what was reported recovered on Friday.
• Four of 27 water samples show "trace amounts of hydrocarbons" in the Willard Reservoir, according to the Utah Division of Water Quality. John Whitehead, assistant director of DWQ, said the data is preliminary, helping "frame the overall picture of the spill and its impact."
"It's too early to say with certainty what the trends are," he said, "but we will continue to monitor daily."
DWQ toxicologist Chris Bittner said the low concentrations pose no concern to people or aquatic life.
"Based on our preliminary data," he said, "use of the reservoir water as a drinking water source, and any recreational uses such as swimming and fishing are safe."
The sampling results, the cleanup's progress and the beavers' discovery are signs that the cleanup is making progress at a crucial time the days before warblers and other migratory birds begin to descend on the internationally renowned habitat up and down the Great Salt Lake's eastern edge.
Although tundra swans, snow geese and pelicans have already been spotted in the area, thousands more are expected to drop in soon for food, rest and nesting.
Biologists hope the cleanup crews can help protect birds from contamination by scaring them away with their activities. Around 100 cleanup workers and about 50 local, state and federal personnel are part of the effort, some of them on the scene only part of the time.
"They're going to go somewhere else, so they are not going to be imperiled here," Walker said of the birds.
An important concern now is making sure the cleanup itself does not harm the wetlands further, said Chris Cline, a U.S. Fish and Wildlife Service biologist who worked on the big BP oil Gulf Coast spill in 2010 and the Yellowstone oil spill in Montana in 2011.
She explained, for instance, it is important to figure out what willows need to be trimmed and which ones need to stay put to preserve the habitat.
"It's a complicated question," she said. "You need input from everybody involved. You don't want to ready, fire, aim. This is the aiming part."
This is the third major petroleum spill from a Chevron pipeline in Utah in three years. Two other spills in 2010 involved a line that released 54,600 gallons of crude oil in Salt Lake City near the University of Utah.
In Utah, Chevron has 657 miles of pipeline, all of it used for hazardous liquids like crude oil and the diesel fuel that travels a 760-mile line from five Salt Lake City refineries to points in Idaho and Washington state.
Walker said he could smell the diesel when he toured the site Monday, a week after the Willard Bay spill was reported. The North Marina has been closed ever since; the South Marina has been opened to accommodate visitors.
Aquatic, wildlife and habitat biologists have been scanning the site daily.
The three new beavers were discovered when a Division of Wildlife Resources biologist stuck a video camera in a beaver lodge and captured fuzzy images of life inside.
How to help
O The nonprofit Wildlife Rehabilitation Center of Northern Utah needs donations of time, money and cuttings of cottonwood, willows and aspen to help with the six beavers, victims of the diesel spill, in its care. Volunteers can contact the center at 801-814-7888. Cuttings can be taken to the center in Ogden at 1490 Park Blvd. Visit the website wrcnu.org to donate money.