Biological Opinions - Bureau of Reclamation

concentrations reach about 2 mg/L, and by about 1.5 mg/L most suckers die (Martin and Saiki
1999). The lethal DO threshold for adult suckers is unknown, but likely is similar to juveniles.
In tributaries to UKL, limited data indicate that DO varies from greater than 7 to 13 mg/L
(ODEQ 2002). Concentrations in the lakes within the recovery unit exhibit seasonal and spatial
variability, ranging from less than 4 mg/L to greater than 10 mg/L. Water quality datasets
collected by the Klamath tribes include weeks during the summer months when DO levels in
UKL are consistently below the ODEQ criterion of 5.5 mg/L for support of warm-water aquatic
life (Kann 2010). Low (0 to 4 mg/L) DO concentrations occur most frequently in August, the
period of declining algal blooms and warm water temperatures in the lake (Walker 2001, ODEQ
2002). Morace (2007) provided a detailed review of DO concentrations in UKL, based on 17
years of data (1990–2006), and Jassby and Kann (2010) conducted a similar review based on an
additional 3 years (1990–2009) of data collection.
Downstream in Keno Reservoir, DO reaches very low levels (< 1 to 2 mg/L) during July and
October as algae transported from UKL settle out of the water and decay. Persistent low DO
events in this reach, where the DO remains less than 2 mg/L, can last for several days or even
weeks. Decomposition of algae transported from UKL appears to be the primary driver of low
oxygen in the Keno Reservoir. Two water treatment facilities discharge treated wastewater to
the Keno Reservoir; however, these facilities contribute a very small amount (100 percent saturation) in surface waters (due to high rates of internal
photosynthesis by algae) and oxygen depletion in bottom waters (due to microbial decomposition
of dead algae). Although J.C. Boyle Reservoir, a relatively long shallow reservoir, does not
stratify, large variations in DO are observed at its discharge due to high oxygen demand from
water conditions in the upstream reach from Link River Dam through the Keno Reservoir, and in
UKL. Copco 1 and Iron Gate Reservoirs thermally stratify beginning in April/May and do not
mix again until October/November (FERC 2007). DO in Iron Gate and Copco 1 surface waters
during summer months is generally at or, in some cases, above saturation, while levels in
hypolimnetic waters reach minimum values near 0 mg/L by July (Raymond 2008, 2009, 2010).
7.10.1.3 Ammonia Toxicity
Low DO events are often associated with high levels of un-ionized ammonia, which is toxic to
fish at concentrations above 0.5 mg/L (Saiki et al. 1999, PacifiCorp 2004, Deas and Vaughn
2006, ODEQ 2010, Sullivan et al. 2011). Ammonia toxicity is complex because it is a function
of both pH and temperature, and is most toxic at higher pH (USEPA 2009). At a pH above 8,
ammonia toxicity is mostly due to un-ionized ammonia, but below pH 8 toxicity is based on total
ammonia concentrations. Saiki et al. (1999) reviewed the results of a variety of tests using
ammonia alone and in conjunction with pH, DO, and temperature to assess how ammonia
affected survival of larval and juvenile suckers, and found that median LC 50 (the concentration of
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