Around 80 birds have been found dead at an oil-contaminated wastewater pond at a Sinclair Oil refinery in southern Wyoming.
The dead waterfowl began turning up Sunday, and Salt Lake City-based Sinclair informed state and federal officials, refinery Manager Mike Bellinger said Friday.
More dead birds turned up as the week went on. Most, if not all, have been western grebes, a black-and-white species that eats fish and ranges across much of western North America.
Bellinger suggested the oil contamination might not have killed the birds.
"They've been deceased for a while, a lot of them," Bellinger said. "We have a biologist working with us to try to determine what exactly is the issue with a lot of them."
But Pete Ramirez, an environmental contaminant specialist with the U.S. Fish and Wildlife Service, said it appeared to him that the birds died recently. He said they landed on the pond ahead of a front that moved in Sunday.
"Unfortunately there was oil on the pond, and it doesn't take much oil to debilitate a bird," Ramirez said.
Rescuers were able to clean up and release around 15 birds, he said.
How much oil was spilled and for how long remains unknown, said Charlie Plymale, an investigator with the state Department of Environmental Quality.
The oil was suspended in the wastewater -- neither floating nor sinking. Barriers were placed along a ditch leading to the wastewater, Plymale said, and trucks were vacuuming oil off the pond and cleaning it up from the shore.
The oil reached the pond after passing through a wastewater treatment facility but the source isn't known yet.
"They're working on narrowing it down, and right now, one of the biggest concerns is the birds," Plymale said.
Meanwhile, Sinclair has set up strobe lights and noisemakers to frighten off any other birds.
"I hope it works," Ramirez said. "It's going to take a lot of effort to keep birds from landing there."
The spill occurred nearly a year after a tank at the refinery ruptured and spilled nearly 3 million gallons of gasoline blend. The Department of Environmental Quality has fined Sinclair $660,000 for the spill.