152 BULLETIN OF THE BUREAU OF FISHERIES. 



Upper Twin Lake at its usual stage of water about midsummer has an area of 

 about 474.5 acres (192 hectares) and Lower Lake about 1,440 acres (5S2 hectares). 

 Both lakes were, no doubt, considerably larger during their earlier stages. The 

 portion of Lake Creek below Lower Lake has worn a channel over 23 feet (6 meters) 

 deep through the old terminal moraine, and it therefore seems probable that the lake 

 was several feet deeper at some time in its past history, which greater depth would 

 increase its size very materially. An increase in the depth of Lower Lake would 

 soon affect Upper Lake also, as the fall between the two is only about 6 or 7 feet (2 

 meters). Moreover, Upper Lake, at no distant time, geologically speaking, probably 

 extended much farther west than it does at the present time. The debris brought 

 down by the various streams that flow into its western end has formed a swampy 

 7neadow of considerable extent, and it seems probable that much, if not all, of this 

 area was covered with water during the early history of the lake, and thus constituted 

 a part of it. 



DEPTH AND VARIATION IN LEVEL. 



In Hayden's Report for 1873, figure 11 is a sketch map showing the results of a 

 number of soundings in each lake. The greatest depths found by him were 79 feet 

 (24 meters) in Upper Lake and 76 feet (23 meters) in Lower Lake. Powell also pub- 

 lished a map of the lakes (1891, pi. lxxxi). He states that 44 soundings were made 

 in Upper Lake and 86 in Lower Lake but gives no results in figures. 



In the present investigations 94 soundings were made in Upper Lake and 85 in 

 Lower Lake, the lines being run in a general north and south direction across each 

 lake in order to make them as short as possible and thus reduce the chance of error 

 to a minimum. On July 8, 1902, the greatest depth found in Upper Lake was 82 

 feet (25 meters) and two weeks later the maximum depth found in Lower Lake was 

 74 feet (22.5 meters). When these soundings were made the water in Upper Lake 

 was at about its normal stage, but Lower Lake was about a foot lower than usual 

 at this time of year. AVhile the maximum depth of Lower Lake is onlv 8 feet (2.5 

 meters) less than that of Upper Lake, its average depth is very much less, as much 

 of the eastern half of Lower Lake is comparatively shallow. 



It was impossible to determine the natural fiuctuation in the level of the lakes. 

 Since the spring of 1901 they have been used as a storage reservoir by the Twin 

 Lakes Reservoir Company. The surplus water of the basin is stored here during the 

 flood season and later is withdrawn for the purpose of irrigating lands in the vicinity 

 of Sugar City, Colo. A dam 18.5 feet (5.6 meters) high is now maintained in the 

 old outlet and the present outlet is a canal. The dam and the canal are so constructed 

 that there is a difference of 25.5 feet (7.8 meters) between extreme high water and 

 extreme low water in Lower Lake. The possible variation in the level of Upper 

 Lake is about 6 or 7 feet (2 meters) less, as already indicated. It is proposed, how- 

 ever, to dredge the creek connecting the two lakes so that they may have the same 

 possible fluctuation in level. Concerning the natural fiuctuation in level previous to 

 the building of the dam, Powell stated, in 1891, "it is not likely that the surface 

 of the lakes varies more than 2 feet in altitude during the year." 



