DESCRIBING LAKE CHARACTERISTICS 



By measurements made entirely on aerial photos, lakes can be described in terms of 

 (1) type, (2) size, (3) elevation, (4) depth, (5) clarity of water, and (6) shore cover. Descrip- 

 tion of bottom material, water temperature, forms of aquatic vegetation, and fish life is not 

 possible from aerial photographs. 



The extent to which lakes are studied and classified depends primarily on the intensity of 

 the survey to be made. In this study, lakes larger than 1 acre warrant description according to 

 type, acreage, depth, clarity, and shore cover. Smaller lakes usually require type and size 

 classification only. 



Lake Type 



Five lake types were recognized in the study area. In other geographic regions, additional 

 or different lake types may be appropriate. The following type classes were used: 



1. Cirque lakes --those in the cirque basins formed at the head of former glaciers. 



2. Moraine lakes --those formed behind the terminal or lateral moraines left by former 

 glaciers . 



3. Reservoirs --lakes formed or altered in level by human activity. Reservoirs can be 

 recognized by the amount of shoreline exposed by fluctuating water levels. 



4. Beaver ponds --small impoundments created when watercourses are dammed by 

 beaver . 



5. Potholes --small depressions formed by disintegrating glaciers and retaining less than 

 1 acre of water. 



The last two lake types are the most difficult to identify because they are frequently simi- 

 lar in size. However, it is desirable to distinguish between them, because beaver ponds are 

 not so permanent as other lakes (spring runoff frequently breaks beaver dams), and because 

 they have different recreational values. Beaver ponds provide fishpools, and the higher water 

 temperatures in the ponds usually allow fish to multiply more rapidly than they generally do in 

 the cold mountain streams. On the other hand, potholes may not support game fish, but they 

 occur in significant numbers and often serve as reflection pools, thus helping to create attract- 

 ive surroundings for hiking and camping. Some pothole lakes are occupied by beaver, and 

 beaver houses may be visible on photos. Because such impoimdments are not created by beaver, 

 they should be classified as potholes rather than beaver ponds. 



In general, beaver -formed ponds are associated with flowing water of small streams 

 (fig. 3). They tend to photograph in medium or light tones of gray^ and can generally be recog- 

 nized by the characteristic fan -shaped pool behind the dam. A ripple of "white water" flowing 

 over the crest of the dam is sometimes visible on the photo. Recognizable beaver houses may 

 provide an additional clue. In contrast to beaver ponds, potholes usually occur in groups in the 

 glacial dumps of terminal and lateral moraines or in glacier -scarred basins. These depres- 

 sions often contain substantial amounts of organic matter, and the ponds thus tend to photograph 

 in darker tones than do beaver ponds. 



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