EUGENE, Ore. — Unusually warm water has killed more than 150,000 summer steelhead fingerlings at an Umpqua River hatchery.
Many more may still die, potentially as much as 95 percent of this year’s batch, Rock Creek Hatchery manager Dan Meyer said.
Hot water is itself dangerous for fish, but it also creates an environment where bacteria and parasites can thrive.
Although the fish were treated in smaller holding tanks and returned to health when the problem was detected, disease broke out again once they were moved back outside.
Hot weather and below-normal snowmelt have steeply raised water temperatures.
Water in the North Umpqua has reached 71.4 degrees this summer, compared to the mid-60s readings that used to mark record highs, Meyer said.
“I have never seen water this warm out of the North Umpqua — I hope this is not the new normal,” he said. “Every year is different, but I have heard that five of the last 10 years have been the warmest in 125 years of record-keeping.”
The die-off the Rock Creek hatchery’s summer steelhead fingerlings peaked during a nine-day period in mid-July.
He doesn’t know how many of the tiny fish there are in the 20-foot by 80-foot raceway where they are contained as they grow and mature enough to be released into the river. Fisheries biologists usually do their population counts in the fall, when the fish are larger and more mature.
Cooling the water — 500 gallons per minute flows through the raceway — would be too expensive, Meyer said.
The loss in such great numbers is a blow, Meyer said.
“It’s not only a big economic hit, it’s like a piece of us goes away too,” he said. “I’ve seen many grown-ups cry over much lesser incidents than this.”
