8o THE TROUT 



consideration ; for, when deepening channels, much 

 bottom-feed is unavoidably destroyed, as well as the 

 roots of many weeds, water plants, &c., these latter 

 being essential to the welfare of the fish. 



Where there are long, still pieces of water, a few 

 half-dams may, very likely, with advantage, be in- 

 serted. These are constructed of two or three upright 

 posts driven into the bottom of the river, to which 

 planks are attached on the up-stream side, the top 

 board being movable, as it may be necessary to shift 

 it should there come a heavy flood. 



The object of these half-dams is slightly to 

 divert the current of the river from its usual placid, 

 level flow, so as to create more movement, and some 

 broken water. 



For this reason half-dams are generally inserted 

 in pairs, on opposite sides of the stream, one being 

 about ten yards higher up the river than the other. 

 They should project a sufficient distance from the 

 bank to create by their joint presence not only a 

 swirling stream, but two backwaters, one behind 

 either dam, which are always sure * holds ' for trout, 

 and those usually large ones. 



To be thoroughly satisfactory as a trouting 

 stream, a river should be possessed of a fair share of 

 gravelly lengths on which the trout can spawn, as 



