DEVILS LAKE, NOETH DAKOTA. 



13 



during a period of rapid development of the surrounding farm 

 lands, which absorb a considerable part of the precipitation. The 

 destruction of spawning beds by the drying of Souris or Mouse 

 River as the result of cultivation of its banks is generally conceded 

 to be one of the principal causes for the disappearance of fish from 

 the waters of Devils Lake. 



TEMPERATTTRE RECORDS. 



During the investigations described by this report daily observa- 

 tions were made of the air and water temperatures from July 26 to 

 September 4, 1907. Readings w^ere made at 8 a. m. and 8 p. m. dur- 

 ing July, and at 8 a. m, and 7 p. m. during August and September. 



The results of these observations, briefly tabulated, are : 



Dates (inclusive) . 



July 26-31 



August !-]:')_. . 



August 16-31.. 

 September 1-5 



Average tempera- 

 ture of air. 



' a. m. 

 64.32 



62.8 

 59.37 



56.0 



8 p. m. 

 70.0 



71.0 

 68.18 

 7 p. in. 

 68.3 



Average tempera- 

 ture of water. 



a. m. 

 69.83 



67.0 

 63.62 



8 p. m. 



72.75 

 7 p. m. 



68.73 

 65.28 



66.0 



Other observations were made at irregular intervals, both in time 

 and locality, during the examination of the lake, especially when 

 running lines of soundings. 



From the maximum and minimum thermometers set up at the 

 headquarters of the party the following averages were obtained. 

 Readings were taken daily at 7.30 p. m., and the instruments were 

 placed in a protected position : 



Dates (inclusive). 



July«5-31... 

 August 1-15, 

 August 16-31 



The lowest temperature recorded was 42°, the highest 88°. 



The importance of temperature in relation to fish culture and 

 maintenance can not be overestimated. In the Devils Lake region the 

 difference between the mean temperatures of summer and winter is 

 very great, the winters being very cold and the summers, in part, hot. 

 During the months of July and August the mornings and nights are 

 cool, the midday delightful. In winter the temperature is continu- 

 ously below zero (Fahrenheit), but the dryness of the air makes the 

 extreme cold (0° to — 43°) more endurable than the higher tempera- 

 tures of a more humid region. 



