61 



pendicularly or at an acute angle at 3-foot intervals along 

 the slope. Water flowing down the incline on striking these 

 projections rises in wave-like crests. The alewives take these 

 steps in a continuous passage by a series of rapid jumps. 

 This fishway is satisfactory, provided that it is not too long, 

 and that the slope is no greater than 1 to 10. Another 

 type has the crosspieces alternately set at an acute angle to the 

 sides, thus retarding the sweep of the water. The Brackett 

 fishway is more satisfactory, as it affords resting places for 

 the fish, and insures easy progress. There are numerous 

 fish ways on the market labeled with the inventors' names, 

 all of which under certain conditions are more or less suc- 

 cessful. 



Installation. The chief point to remember is that it is not 

 the type of fishway, but the way in which it is installed which 

 determines its success or failure, since each dam presents cer- 

 tain peculiarities which necessitate individual treatment. In 

 installing a fishway the following conditions must be con- 

 sidered : 



(1) Water Flow. Provision for a constant flow of water, 

 irrespective of variations in the level of the pond, can be made 

 by (1) an adjustable upper section of the fishway to correspond 

 to the water level, (2) a gate situated at the lowest probable 

 water line; and (3) several gates at different levels. 



(2) Entrance. Instinctively the fish follow the greatest flow 

 of water, usually up the main stream to the dam. Therefore 

 either the entrance must be directly beneath the dam, where 

 the fish will naturally swing into it, or there must be some 

 means of directing them. Screening the stream with an iron 

 grating is a successful though expensive method. A submerged 

 stone barrier leading to the fishway entrance has proved at 

 times effective. 



(3) Construction. The nature of the soil and height of the 

 dam largely influence the difficulty and expense of construction, 

 necessitating a careful survey before exact plans are submitted. 



(4) Destruction. Destruction of a fishway by spring floods 

 may be partially avoided by (1) building a concrete structure; 

 (2) locating the fishway where it is subject to the least damage; 

 and (3) having part or all removable when not in use. 



