4 IOWA STUDIES IN NATURAL HISTORY 



The region about lake Okoboji and the lake itself was 

 surveyed by the civil engineering department of Iowa State 

 College through its summer surveying camp. The camp 

 was held there from 1905 to 1912, and the topography of 

 the region and the hydrography of the larger lakes were 

 surveyed. In 1913 a pamphlet was published by the Col- 

 lege (Ford '13) giving the methods employed, together with 

 maps showing the results. Among the maps are a topo- 

 graphical map of the region on a scale of 1 in. to 5100 ft., 

 and a map giving the soundings in Okoboji lake on a scale 

 of 1 in. to 2500 ft. The College also kindly furnished us 

 with a blue print map of the lake, scale 1 in. to 1000 ft., 

 which was used in all measurements. This map was repro- 

 duced in the Iowa report on lakes and lake beds on a scale 

 of about 1 in. to 2030 ft. In this report about one page of 

 description is given to the lake and its area is stated as 

 3788 acres (Iowa '16, p. 56, map No. 18)* The area thus 

 given is accepted in this paper. 



The small scale map of the lake gives all of the sound- 

 ings, numbering 732, or about 48 per sq. km. The large 

 scale map gives a selection of these, numbering 261. The 

 soundings were taken from a motor boat which was kept 

 constantly in motion. Its position at the moment of sound- 

 ing was signalled to two observers on shore who kept the 

 boat constantly in sight with transits. By this method the 

 position of the boat could hardly have been determined with 

 minute accuracy, especially in the deeper water, and the 

 maps give no dot or other similar indication of the precise 

 position of the soundings. It is known that the small area 

 which contains the deepest soundings lies somewhat to the 

 west of the place indicated on the map. Under these con- 

 ditions no attempt was made to plat the soundings omitted 

 on the large scale map. In drawing the contours for the 

 hydrography a 20-foot interval was used, since there are not 

 enough soundings along the shores to warrant the use of 

 a 10-foot interval. 



The areas included in the several contours were measured 

 with the planimeter, with the following result: 



* Note: Appended to this article as Plate I. 



