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Caption: The USFWS found dissolved oxygen (D.O.) levels as low as 3.1 mg/l at its Big Bar downstream migrant trap below Orleans on August 9, 1997. D.O. levels of less than 5 mg/l are stressful for salmonids and those less than 4 mg/l are lethal. The all night monitoring was instituted when warm water species, such as speckled dace and Klamath large-scale suckers, were found dead in the USFWS downstream migrant trap. Note that D.O. starts to drop in evening hours after 8 P.M. (20 on chart). Once algae and other aquatic plants begin to photosynthesize, D.O. levels rise. This pattern strongly suggests that dissolved oxygen pattern in the mainstem Klamath were driven by entrained algae. Click on the Info Links tab for more information or see Halstead, 1997 in the Bibliography.
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