IMPROVEMENT OF LAKES AND STREAMS 39 



Improvement consists in remedying the conditions found to be most 

 unsatisfactory, as far as the results will justify the expense. Most im- 

 portant is the maintenance of a flow of pure water uncontaminated by 

 sewage or by refuse from industrial operations. Silt from eroded water- 

 sheds must be reduced, because it smothers the food organisms, destroys 

 spawning beds, fills up pools, and sometimes even smothers the fishes 

 themselves. The silt in streams can be controlled by stopping soil 

 erosion in the cultivated fields of the drainage basin. 



The construction of deflectors and various types of dams may direct 

 and concentrate currents so that they will sweep silt downstream and 

 also will wash out holes, providing more of the deeper waters for the 

 larger fishes. Many small streams are so shallow that they may freeze 

 to the bottom in winter. Judicial regulation of current and depth may 

 eliminate deep freezing. 



In many trout streams the maintenance of low temperatures is one 

 of the greatest problems. Trout do best in water with summer tempera- 

 tures ranging from 50° to 65° F. The destruction of shade along the 

 banks may allow the sun to warm the water until it becomes too warm 

 for trout. In such places shade should be restored by planting trees or 

 bushes. The stream may be narrowed and the current forced into the 

 shady part. A cover of bushes and brush may be pulled over the stream. 

 The water can be further cooled by cleaning and enlarging any lateral 

 feeder springs. The few streams that are too cold may be warmed by 

 widening them with dams to spread out the water and expose it to the 

 sun. 



Spawning conditions may be improved in almost every stream. All 

 trout require coarse gravel beds for spawning. In streams with bottoms 

 of soft mud and sand, spawning beds of coarse gravel may be con- 

 structed at intervals. Spawning conditions can be greatly improved by 

 opening small lateral feeder streams and building spawning beds. 



Good trout waters have alternate pools and rapids. Most of the 

 aquatic insects that form an important part of the diet of trout are 

 produced on beds of coarse gravel and small boulders. Sand and solid 

 rock are low in food production. Weed beds on silt bottoms produce 

 large quantities of small Crustacea and insects and are important assets 

 for increased productivity. For best results a trout stream should have 

 ample feeding beds with sheltered water easily accessible. 



Long straight stretches of swift water may produce abundant food 

 but are usually barren of trout, which need pools for shelter. Pools can 

 be made in streams by damming with logs and rocks. If the pools are 

 too deep, suckers and other fishes may enter and compete. Too many 

 pools mean a shortage of swift water, in which many of the food or- 

 ganisms develop. Pools should be sheltered with overhanging banks or 

 logs. Small trout need weed beds for feeding and cover, and such beds 



