Authorities for now are focusing on the city's wastewater treatment plant in their investigation into what abruptly killed about 100 small fish in lower Ashland Creek, despite city officials so far finding no indication the plant was involved.
First discovered Sunday, the dead juvenile wild steelhead and other species were part of what is likely the worst known fish-kill in the Bear Creek Basin in five years, records show.
Investigators found them along a third-of-a-mile stretch from the creek's confluence with Bear Creek upstream to the location where the plant's treated effluent is released into the creek.
With no dead fish discovered above the plant's release site, state Department of Environmental Quality officials have asked the city to look more closely at plant gauges and records and add new tests to see whether something was amiss there, said Bill Meyers, the DEQ's water-quality specialist in the Rogue River Basin.
City officials Monday checked plant records and found no change in oxygen or toxicity levels to indicate the plant's effluent had anything to do with the dead fish, but they are planning a battery of new water-quality tests as part of the investigation.
"All of us are scratching our heads," Ashland Director of Public Works Mike Faught said Tuesday. "There's nothing at the plant that would indicate that it came from the plant."
Meanwhile, a small sampling of the dead fish was sent Tuesday to the Oregon Department of Fish and Wildlife's fish pathology lab for testing.
Those tests will look at whether any growths, lesions or other fish-health problems contributed to the die-off, said Dan VanDyke, Rogue District fish biologist for ODFW.
VanDyke walked the creek stretch Monday and discovered an unreported number of dead juvenile steelhead and sculpin along with a few wild chinook and one red-sided shiner. All but the shiner are native to the Bear Creek Basin.
So far, no native coho salmon have been identified in the die-off, VanDyke said.
The Rogue's wild coho are listed as a threatened species under the federal Endangered Species Act and it can be a federal crime to harm or harass them without federal permission.
VanDyke said he did not discover any freshly killed fish there Monday, indicating the possibility of an isolated pollution event over the weekend.
Biologists were back in the field late Tuesday to see whether they could find any more dead fish in Bear Creek downstream from the Ashland Creek mouth.
VanDyke said his agency was conducting a natural-resource damage assessment, during which time the ODFW typically does not release preliminary counts. In past fish kills that ended up in court cases, the release of preliminary counts has harmed the agency's ability to collect damages for fish losses, VanDyke said.
Faught said he believed the dead fish numbered about 100, but that no one knows what the overall tally was.
If so, that would make it the largest known abrupt fish-kill in the Bear Creek Basin since 2007, when about 100 wild juvenile steelhead and coho were found dead in lower Griffin Creek from an apparent petroleum release into the creek, records show. The source of that die-off was never pinpointed and no one was prosecuted.
Reach Mail Tribune reporter Mark Freeman at 541-776-4470, or email at firstname.lastname@example.org.