Biological Opinions - Bureau of Reclamation

overall flow volume in the river. However, the slight decrease in water temperatures in this
reach is generally not sufficient to support cold-water fish habitat during summer months. Daily
maximum summer water temperatures have been measured at values greater than 78.8 °F (26°C)
just upstream from the confluence with the Trinity River (Weitchpec [RM 43.5]), decreasing to
76.1 °F (24.5 °C) near Turwar Creek (RM 5.8; Yurok Tribe Environmental Program 2005,
Sinnott 2010).
11.3.1.1.2 Dissolved Oxygen
Based upon measurements collected immediately downstream from IGD, dissolved oxygen
concentrations regularly fall below 8 mg/L (Karuk Tribe of California 2001, 2002, 2007, 2009).
Continuous sonde data collected at other Klamath River locations downstream from IGD during
the summers of 2004 to 2006 show that roughly 45 to 65 percent of measurements immediately
downstream from the dam did not achieve 8 mg/L. Daily fluctuations of up to 2 mg/L measured
in the Klamath River downstream from IGD (RM 190) have been attributed to daytime algal
photosynthesis and nighttime bacterial respiration (Karuk Tribe of California 2002, 2003; Yurok
Tribe Environmental Program 2005; NCRWQCB 2010). Farther downstream in the mainstem
Klamath River near Seiad Valley (RM 129), dissolved oxygen concentrations are higher than the
reach immediately downstream from IGD, but are variable with mean daily values ranging from
approximately 6.5 mg/L to supersaturated concentrations of approximately 10.5 mg/L, from June
through November 2001 to 2002 and 2006 to 2009 (Karuk Tribe of California 2001, 2002, 2007,
2009).
Measured concentrations of dissolved oxygen in the mainstem Klamath River downstream from
Seiad Valley (RM 129) continue to increase with increasing distance from IGD (Figure 11.1).
Dissolved oxygen concentrations near Orleans (RM 59) continue to be variable, with typical
daily values ranging from approximately 6.5 mg/L to supersaturated concentrations of 11.5 mg/L
from June through November, 2001 to 2002 and 2006 to 2009 (Karuk Tribe of California 2001,
2002, 2007, 2009; NCRWQCB 2010; Ward and Armstrong 2010). Farther downstream, near the
confluence with the Trinity River (RM 43) and at the Turwar gage (RM 5.8), minimum dissolved
oxygen concentrations below 8 mg/L have been observed for extended periods of time during
late summer/early fall (Yurok Tribe Environmental Program 2005, Sinnott 2010, Asarian and
Kann 2013).
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