Biological Opinions - Bureau of Reclamation

We assume that UKL surface elevations are less critical to adult suckers during November
through February because they redistribute throughout the lake after water quality in the lake
improves and as lake levels increase through the winter (Banish et al. 2007, 2009), as a result of
reduced water diversions and increased inflows.
As discussed above, the USFWS concludes that the proposed Project operations are likely to
provide adequate habitat for older juvenile and adult suckers during most years because there
will be sufficient water depths. It is only when UKL levels are equal to or less than 4,138.2 ft
(1,261.3 m) at the end of September and water depths become so shallow that there is loss of
some preferred habitats that there is likely to be adverse effects to these age classes. Such lake
levels occur 3 years out of 31 years in September (Table 8.1) based on the POR modeling, and
thus these elevations are expected to be rare events and are not expected to limit the persistence
of older juvenile and adult LRS and SNS.
8.3.1.6 Effects to UKL Water Quality
UKL has experienced serious water quality events in the past that have resulted in massive fish
die-offs, including thousands of LRSs and SNSs, as well as pronounced redistribution of fish
(Buettner and Scoppettone 1990; Perkins et al. 2000b; Banish et al. 2007, 2009). In UKL, water
quality poses the greatest threat to all fish from July to mid-October, but especially late July and
August (Wood et al. 1996, Kann 1997, Perkins et al. 2000b, Loftus 2001, Welch and Burke
2001, Wood et al 2006, Morace 2007, B. Martin, USGS, pers. comm. 2013).
One of the questions that has been raised in relation to Reclamation’s management of UKL is:
how do lake levels affect water quality (USFWS 2001, 2001, 2008)? A number of possible
mechanisms relating lake depth to water quality have been proposed, such as effects on nutrient
concentrations that drive algal productivity that subsequently affect DO and ammonia
concentrations (Wood et al. 1996, Reiser et al. 2001, Morace 2007; USFWS 2002, 2008).
However, most empirical analyses of water quality data taken from the lake indicate no obvious
and statistically significant connection between UKL levels and water quality over the range at
which the lake is usually managed (4,138 to 4,143 ft [1,261 to 1,263 m]; Wood et al. 1996,
Morace 2007). However, Jassby and Kann (2010) did document a statistically significant
association between chlorophyll-a levels in UKL and water elevations for the months of May
and June.
Wood et al. (1996) concluded that there was no evidence of a relationship between any of the
water quality variables considered (i.e., chlorophyll-a, DO, pH, total phosphorus) and lake depth
based on an analysis of the seasonal distribution of data or a seasonal summary statistic. The
analysis found that low DO, high pH, high phosphorus concentrations, and heavy AFA blooms
were observed every year regardless of lake depth. Morace (2007) repeated this analysis using
11 additional years of data from UKL, and also did not detect a statistically significant
relationship between lake depth and water quality. However, this does not mean that water depth
has no effect on water quality, only that existing empirical data and analyses have not shown an
observable, statistically significant relationship between UKL levels and water quality over the
range of depths that UKL has been operated at during the 1990–2006 period. The National
Research Council (2004) also did not identify a quantifiable relationship between UKL depth
146