FISHES OF COLORADO 7 



fauna. For the study of the fishes found in them the waters of 

 Colorado may be divided into two groups, the river systems and the 

 lakes. 



River Systems 



Two features of the river systems of the state, taken collectively, 

 are particularly noteworthy: (a) three distinct drainages are repre- 

 sented, the Mississippi, the Rio Grande and the Colorado; (b) all of 

 the large streams of the state have their headwaters in the mountains 

 within the state. Both the diversity of drainage areas and the large 

 number of headwater streams are the result of the presence of the 

 Continental Divide in central Colorado, separating the lower, eastern 

 and western portions. This division of the land areas by the moun- 

 tains has a very important bearing on the fish fauna as a whole, since 

 often many of the fishes of independent drainages are different, and 

 the conditions to which fishes are subjected in the headwater streams 

 are always more rigorous than in the lowland streams. The position 

 of the mountains in Colorado is also responsible for the direction of 

 the larger streams, these flowing east or west, while their tributaries 

 enter from the north and south. 



I. The Mississippi System. — This drainage in Colorado includes 

 all of the streams east of the Continental Divide excepting the Rio 

 Grande and its tributaries, and comprises the North Platte, the South 

 Platte, the Republican and the Arkansas, with their tributaries. 



The North Platte drains a high mountain park. North Park, 

 inclosed by the Continental Divide on the south and west and the 

 Medicine Bow Range on the east. The Colorado portion of this 

 stream is entirely a mountain stream since it does not fall below the 

 8,000-foot contour and is fed from the snows on the surrounding 

 mountains. 



The South Platte and its tributaries drain roughly the north- 

 eastern quarter of the state, about 22,000 square miles in all, of which 

 more than 12,000 square miles are below the 6,000-foot contour. 

 The main stream, which is more than three hundred miles in length, 

 rises in South Park at an altitude of about 1 1 ,000 feet, so that it is 

 both a mountain and a plains stream in Colorado. Flowing out of 



