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FISHES AND FISHERIES OF NEVADA 183 by that amount. r since Congress he present names mention. in r in certain ways peaces are of two el and (2) more m elevation behind UK east-northeast. constant and con- sic lake conditions deal stratification, uax by controlling pan which all other t water astride the of warming these wx from 360 F. for kind and 31ohave are winter to 80° F. in summer. The warmest part of the lake seems to be the Overton Arm, where surface waters reached maxima of nearly 900 F. in summer, and minima at 50 feet depth of about 510 F. Depths of down to 300 feet, farther south in the Overton Arm did not quite achieve these minima. The often sharp differences between lake and river waters produce striking effects where they come together. If river water is colder than that of the lake, it may slide under the warmer lake waters for con- siderable distances without appreciable mixing. If river water is the ± AVC S -ice Y?' ti s. lx - L fJ k I IS -ev Fro. 60. Hoover (Boulder) Pam. Clark County, looking north at the mouth of Black Canon. Courtesy Nevada Highway Department and Adrian Atwater. warmest of the two, the reverse effect occurs. While, from a physical point of view, the interrelations between such water bodies with differ- ing temperatures is quite complex, these seem to have little or no meognizable effects on the fishery. In the Forel-`'Whipple system of lake classification, Mead would resemble a tropical lake of the third order-with surface waters never dropping to 40 C. and with circulation more extensive than the usual winter period. As in the case of Pyramid and other Nevada lakes, Forel's original attempt to categorize lakes-later modified by Whipple -httx to be altered further before it can be applied to most of our major bodies of water. Heveral investigators have noted the occurrence of a thermocline in Lake Mead, among them illoffett (1943: 180) and Sumner (Jonez and It