140 BULLETIN OF THE BUREAU OF FISHERIES. 



doubtless, be found in the high specific heat of water, the great depth of the lake. 

 and in the agitation of its waters by the strong winds of winter." (Le Conte, 1883, 

 p. 511.) 



Transparency. — Lake Tahoe is noted for its clear, transparent water. On calm, 

 sunny days, objects could be distinctly seen on the bottom where the water was 50 

 feet deep. In fact, these objects were so plainly visible that the water did not appear 

 to have a depth of more than 10 or 15 feet. A Secchi's disk, 5 inches in diameter, 

 just disappeared from view at a depth of 65 feet. Le Conte (1883, p. 512) found the 

 water much more transparent, however, as he says that a dinner plate 9.5 inches in 

 diameter was plainly visible at a depth of 108 feet. The lower degree of transpar- 

 ency found by me was probably due to the fact that my observations were made 

 during the flood season. All the affluents were filled to overflowing and had been for 

 some time previous to this. These swollen streams were invariably more or less 

 roily, and at the mouths of the larger ones the sediment-bearing water could be traced 

 into the lake for some distance. 



One of the most striking features of the lake is the great diversity of color exhib- 

 ited by the water. " It appears that under various conditions — such as depth, purity, 

 state of sky, and color of the bottom — the waters of this lake manifest nearly all 

 the chromatic tints presented in the solar spectrum between greenish yellow and the 

 darkest ultramarine blue, bordering upon blue black." (Le Conte, 1883, p. 596). 



Aquatic vegetation. — The larger forms of aquatic plants were found to be com- 

 paratively scarce. Most of the shore of the lake is of such a nature that it is difficult 

 for them to obtain a foothold. In the more favorable locations such forms as Scirpvs, 

 Batrachium, Potamogeton, Carex, and Nitella were found. 



Tin plankton. — A few plankton hauls were made June 27, 1904, on the west side 

 of the lake, about 2 miles south of Tahoe Tavern, where the water reaches a depth 

 of about -too feet. A comparatively small quantity of plankton was found; the lake 

 would probably be classed as plankton-poor. The phytoplankton was relatively 

 small in amount and consisted of diatoms and filamentous alga-. . 



Only one species of rotifer was noted, Nbtholca longispina Kellicott. It was 

 found in very limited numbers. 



Copepoda made up at least three-quarters of the bulk of the plankton. The lim- 

 netic members of this group were Epischura nevadensis Lilljeborg and a species of 

 Diaptomus. The latter was the most abundant form and constituted over half the 

 entire quantity of plankton. ( 'yclqps was not noted in any of the limnetic catches. 



The ( Iladocera were represented in the limnetic region by two Daphnias. Daphnia 

 pulex De Geer apparently belongs to the variety pulicaria Forbes. It differs from 

 Forbes's description of this variety in a few minor points, the sensory hairs project- 

 ing slightly beyond the tip of the beak, and the eye being somewhat smaller and 

 situated a short distance above the ventral margin of the head. Daphnia hyalina 

 Leydig seems to agree most closely with Burckhardt's variety richardi. The head 

 is small, contained four times in the length of the body, and its ventral contour is 

 moderately concave. The crest is small and regularly curved. The eye is small and 

 situated in the anterior third of the head, a short distance above the ventral margin. 

 The spine is short. 



