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-25- Achnanthes snn. 1Vavicula lanceolate Navicula rhvnchoceAhala Ktz. Amory a ovals Ktz. Rho~:Todia~~ibba (Ehrenb.)O.Mue11. Surinella ovate (Ktz.) CYANOPHYTA - Blue-green algae AAhanocansa elachista W. & G.S. West Oscillatoria animalis Ag. Lsn~bva orcharacea Ktz.) Thuret Microcoleus -~aludosus (Ktz.) Gom. aba asp. fragments frequent Limnolo~y of the Colorado River Due, in part, to the fact that much of the area drained by the Colorado River has little plant cover and has suffered from excessive erosion, the average annual fluctuation of the Colorado River is quite extensive. Measure- ments made by the iJ.S. Geological Survey at gauging stations at Hite and Lees Ferry from October, 1955 to September, 1956, gave the following results: Oct. Nov. Dec. Jan. Feb. Mar. AAr• l~av June July ALi~. Sept. Hite-Avg.monthly 3210 4305 4834 5338 4230 7619 1313© 31270 37470 8138 5010 2697 flow c.f.s. Lees Ferry-Avg. 3476 4632 5309 6065 4876 8306 15090 35620 43590 9054 5786 2791 monthly flow c.f.s. At Hite the maximum flaw of 61,800 c.f.s. occurred on June 6, while a minimum flow of 2,400 c.f.s. occurred on September 17. The volume of water occasionally maximum flows of over 100,000 c.f.s. occur. As a result of the excessive erosion in much of the Colorado River Basin the river is quite tur- bid and highly colored. Much of the turbidity appears to be in the form of silt and sand rather than mud and settles out quite rapidly in water samples. Turbidity determinations made in the river ranged from a high of 380 ppm found near Kane Creek on July 31, 1958, following heavy rains to a low of 30 ppm recorded- near Hite on January 6, 1959 (Table 6). Both color and turbidity were found to be subject to considerable variation. Heavy rains were always found to be followed by an increase in the amount of organic matter washed into the river as well as increased turbidity. In most areas, the river bottom is composed of shifting sand. Riffles and areas with rocky bottoms occasionally occur, usually near the mouths of some of the tributaries. Due to the scouring action and shifting of the sandy bottom rooter aquatic plants were almost completely absent, although xillows and Tamarix were often inundated during high water. Water temperatures show both a diurnal and seasonal fluctuation. During the summer of 1958 water temperatures in excess of 80° F. were re- corded. A water temperature of 33°F was recorded in the river near Kane