GRAYLING OF GREBE LAKE 



309 



GREBE L 



YELLOWSTONE NATIONAL 

 LEOEN 



CONTOUN INTERVAL 3' 

 PENUANENT STATION * 

 INLET I 



ANEA I4S A 



SHONE LINE SONVETEO ST T 

 SOUNOIPNS NT KNUSE. Diinc 

 AND SEIHANOS 



Fkhre 1. — Contour map of Grebe Lake, Yellowstone National Park, Wyo. 



during 1953 (6-ft, depth) or 4° F. in 1954 (1-ft. 

 level). 



Thermal characteristics of Hatchery Creek, one 

 of the inlets, were also recorded by a thermograph 

 in 1953 and 1954 (fig. 4). Average weekly 

 temperatures rose rapidly during June, then, 

 gradually until mid-July. The maximum hourly 

 temperature of 63° F. occurred at 3:00 p. m. on 

 June 18, 1953. The daily peak was readied 

 between 1 :00 p. m. and 5:00 p. m. Daily minima 

 occurred between 5:00 a. m. and 7:00 a. m. 

 The greatest range for a 24-hour period was 23° 

 (June 17, 18, 1953). The highest temperatures 

 occurred in late spring and resulted from flood- 

 water, which flowed in a shallow layer over the 

 meadow surrounding Hatchery Creek, then drained 

 back into the creek bed above the thermograph. 



CHEMICAL FACTORS 



Grebe Lake stratified both thermally and chemi- 

 cally during 1953 and 1954. On July 14, 1953. 



grayling and hybrid trout taken from trap nets 

 set in water more than 20 feet deep were dead or 

 in distress when the nets were lifted, but not so 

 for those in shoal sets. The results of a water 

 chemistry analysis made August 6, 1954, showed 

 that the oxygen concentration in the lake at the 

 20-foot level contained only 4.5 p. p. m. (54.4 

 percent saturation) and decreased to 0.6 p. p. m. 

 (6.8 percent saturation) at a depth of 28 feet 

 (table 1). 



Grebe Lake may be classified as an eutrophie 

 lake with a deficiency of oxygen in its depths 

 during the period of summer stagnation. 



BIOLOGICAL FEATURES 



Three species of plants dominated the vegeta- 

 tion within the lake. Large beds of waterlilies, 

 Nuphar polysepalum, paralleled the eastern shore- 

 line and extended into the lake up to 100 feet. 

 On the bottom between water depths of 4 feet 

 and 15 feet laid a nearlv continuous 2-foot blanket 



