An estimated 109 wild spring Chinook salmon in the upper section of the Middle Fork John Day River died last week, apparently due to low river flows and warm temperatures.
According to Brent Smith, ODFW fish biologist in John Day, water temperatures in the mid-70s combined with low stream flows likely led to the deaths of these fish. Like many rivers across Oregon, stream flows in the Middle Fork John Day have been extremely low this summer.
The spring Chinook die-off was first discovered by ODFW staff on July 7 near Windlass Creek. The following two days more dead fish were observed during a survey conducted over a 17-mile reach downstream of Hwy. 7.
Similar salmon die-offs occurred in 2007 and 2013 with high temperatures being the main cause. The Middle Fork’s lack of riparian vegetation combined with a wide and shallow channel exposes much of the river to direct sunlight which can lead to cause quick rises in water temperature.
Smith said he expects to see additional salmon mortalities for the rest of the summer until spawning occurs in early September. He said the John Day basin as a whole is seeing a strong salmon return this year and recent summer rains have brought some relief.