The heavy silt load in July could be detrimental to the pro- 

 ductivity of the lake by reducing the penetration of the sunlif;ht 

 which is required for growth of phytoplankton. Similar observa- 

 tions should be continued in the future to determine whether 1948 

 was an abnormal year due to its record spring runoff. 



PIANKTON 



Plankton samples were taken whenever water analysis was made at 

 the various stations located on the reservoir. Plankton material 

 was secured by means of a standard type plankton net with a 3-3/4 

 inch orifice, a brass oolleotion bucket, and covered with number 

 20 silk bolting oloth. The procedure used was to lower the net 

 10 meters and slowly raise it to the surface. By standardizing this 

 procedure a rough quantitative comparison among various stations located 

 on the lake was made possible; it was accomplished by inspection of 

 uniform diameter vials containing the preserved plankton. Rather meager 

 hauls at stations upstream as compared to good takes below indicated 

 greater productivity in the downstream portion of the reservoir. This 

 undoubtedly is due to the stream-like nature of the upper section 

 of the reservoir as ocmpared with the deeper, slower-moving section 

 below. 



TA.BLE 7, 1948 Secchi Disk readings Roosevelt Lake, 

 measured in Feet. 



Fish sfiunpling was carried out by means of gill nets at six 

 different locations along the reservoir (Figure 4). Three nets were 

 used; they were 125 feet long by 6 feet deep, and had mesh graded from 



18 



