Water ordinarily is stored in Hebgen starting immediately- 

 after the ice break-up in spring and continued through early August, 

 Snow melt in the Madison watershed is usually more than sufficient to 

 maintain the required volume of water for power production at Madison 

 Reservoir during this period,, Only infrequently is water released 

 during May, June, or July,, Starting in August ai d continuing into 

 the fall, water releases from Hebgen are usually greater than the in- 

 flow and there is a gradual decline in the water level It was 

 necessary to draw most of the water out of the reservoir during the 

 drought period of 1933 and 193U but this was the only really unusual 

 drawdown since creation of the reservoir. Annual drawdown is usually 

 around 10 to 1$ feet. Over the years, erratic fluctuations have been 

 unusual and fish losses due to drawdown have been minimal. 



Surface water temperatures averaged about 55° F, (12° or 

 15° above those in the river below the dam) in the early part of the 

 1952 fishing season. From the latter part of May through mid -September, 

 temperatures usually were over 60° F, The recorded maximum was 66° F, 

 (August) „ 



Except for a short period when a plankton "bloom" occurred, 

 and excepting the Grayling Arm of the reservoir, the water was clear 

 throughout the summer of 1952, The Grayling Arm of the reservoir was 

 extremely murky most of the time, probably because this part of the 

 lake was a bog prior to inundation and much of the bottom material in 

 this area is loose and exists as a false bottom, and causes roiling 

 upon the slightest movement. 



Aquatic vegetation is well established in Hebgen and border- 

 ing marshes. The shallow South Fork Arm had so many pondweeds in 1952 

 as to make boating impractical, Pondweeds also were abundant in the 

 Madison Arm, Timber was not cleared from Hebgen when it was created, 

 and a considerable stretch along the west shore of the Madison Arm 

 now has submerged logs which make fishing, especially trolling, 

 difficult,, 



No bottom fauna studies were made in Hebgen, but general 

 observations indicated an abundance of stone fly nymphs, mayfly 

 nymphs, and dipterous larvae, especially in the weedy areas of the 

 lake. 



Climatic conditions in the Madison Basin are character- 

 istic of the northern Rocky Mountain Region, Owing to the mountainous 

 nature of the basin (elevations varying from U,000 to 11,000 feet), 

 climatic conditions vary widely at different points. The winters are 

 generally severe, with many days of subzero temperature, January 

 temperatures average between 10 and 20° F, The days are generally 

 clear and warm and the nights cool in the summer. Mid-summer tempera- 

 tures average 65° F„ The growing season is relatively short, ranging 



