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` • 12 ~~ ~• too high to project an LC1 or an LC~~; inconsistent data; and complications of test fish deaths due to causes other than toxicant concentrations. In some cases where the LCD's were not determined we can combine data from two or more tests to predict test concentrations of toxicants to use with the Colorado squawfish. Repeat tests will have to be conducted in some instances where the data are considered unreliable or insufficient. In reference to the originally proposed comparisons of pH effect on the toxicity of selected chemicals ~pH 6, 7 and 8}, several problems have become apparent. Normally, one would use a chemical buffer system to adjust pH in static bioassays. In our situation, we are trying to duplicate the water from the natural environment of the Colorado squawfish and in addition, adjust pH to different levels. To reach the lower pH 6 level, such Large amounts of buffer are required that the water chemistry is substantially altered. The result is an invalid test situation for the fish. We therefore recommend Lhat pH effect on toxicity be examined within ranges that can be controlled without•substantially altering the water chemistry of our test water. From our experimentation thus far, we expect the range can be manipulated between pH 7 and. pH 8.5, The impracticality of conducting bioassays with the 3 test waters originally planned was explained earlier in this report. The most useful data we can provide for the toxicity of .selected chemicals to the Colorado i ' squawfish will be by utilizing test water that simulates their natural environment. The location of Willow Beach NFH, lI miles downstream from ~ Hoover Dam, provides an appropriate point in the Colorado River drainage system to duplicate. With respect to the current known range of the Colorado squawfish, Willow Beach is as appropriate as any other point in the drainage that might be chosen. Therefore, until indicated otherwise