Biological Opinions - Bureau of Reclamation

Figure 11.20. Example Mainstem Klamath River channel cross section at river mile 106 near Happy Camp
(Asarian and Kann 2013). Cross section from data in Ayres Associates (1999) for site number 3, cross section
number 5.
High levels of photosynthesis cause dissolved oxygen concentration to rise during the day and
lower at night during plant respiration. Low dissolved oxygen concentration at night reduces
rearing habitat suitability at night. Daily fluctuations of up to 2 mg/L of dissolved oxygen in the
mainstem Klamath River downstream from IGD have been attributed to daytime algal
photosynthesis and nocturnal algal/bacterial respiration (Karuk Tribe of California 2002, 2003;
YTEP 2005, NCRWQCB 2010).
In addition, the overall effect of the conceptual linkages between flow and dissolved oxygen is
supported by an analysis of 11 years of mainstem Klamath River water quality data that found
that higher flows were strongly correlated with higher dissolved oxygen minimums and narrower
daily dissolved oxygen range (Figure 11.21, Asarian and Kann 2013). Therefore, when the
proposed action reduces mainstem flows in the summer, NMFS expects there will likely be a
reduction to dissolved oxygen concentrations in the mainstem Klamath River between IGD and
Orleans (RM 59). The proposed action’s contribution to dissolved oxygen reduction likely
diminishes around Orleans (RM 59) as tributary accretions offset the dissolved oxygen
reductions near this site.
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