June 18, 2015
CLACKAMAS, Ore. – Elevated water temperatures are most likely the cause of spring Chinook salmon deaths in the Willamette River and some of its tributaries, according to fish biologists from the Oregon Department of Fish and Wildlife.
ODFW biologists and survey crews have observed unusually large numbers of spring Chinook salmon carcasses in the Willamette, Clackamas, and Santiam rivers recently.
“Pre-spawning mortality is normal and happens every year to some extent,” said Friesen. “But usually we don’t see dead spring Chinook in the mainstem Willamette until mid-summer.”
ODFW biologists say that high water temperatures likely contributed to the death of the fish.
Chinook salmon are more prone to disease, injury, and stress when water temperatures exceed 60° F. At 70°, the fish start to get into real trouble.
For the past week, water temperatures in the Willamette River have risen steadily, from 70° to 74° F. During the same period, Clackamas River water temperatures rose from 62° to 64° while the Santiam rose from 62° to 66°.
“Fortunately, many of this year’s spring Chinook have already entered the tributaries, which should help ensure their survival,” Friesen said.