FORTIETH BIENNIAL REPORT 33 



The king salmon resource can be increased by erecting suitable fish 

 ladders over those low dams which now prevent the access of the salmon 

 to the spawning areas above, by cleaning up the pollution spots that stop 

 the migrations of both the adults and the young, and by screening the 

 diversions that trap and kill young on their way to the sea. 



During the biennium, considerable progress has been made in the 

 construction of fishwaj^s and screens in the Central Valley, but much 

 remains to be done. We have developed a screen and ladder unit which 

 works in close cooperation with the Division of Architecture. 



The most notable achievement of the past several years was construc- 

 tion of a new fishway at Woodbridge Dam on the Mokelumne River. This 

 stream has been suffering from the effects of a serious fish block at the dam. 

 The old ladder was too small and too steep, was poorly located, and could 

 not be reached by the fish during periods of low flows. When the flash- 

 boards were removed from the dam, the old fish ladder was totally inop- 

 erative, and at low flows the dam was impassable. Because of this situation, 

 the salmon run is badly depleted. In early 1948 the new fishway was com- 

 pleted (see Figure 14). This ladder has two branches, one for use when 

 the flashboards are in place, the other for when the boards are out. The 

 structure was designed and the work supervised by the Department of 

 Public Works, Division of Architecture. Their engineers can well be 

 proud of the result. The fall of 1948 will be the first chance salmon will 

 have to use the new ladder. Rehabilitation of the run can be expected in 

 the next few years. 



In late 1946 a fishway was completed over Clough Dam on Mill Creek. 

 This ladder has since functioned well, and should result in benefit to the 

 salmon and steelhead runs in this important tributary of the Sacramento 

 River. 



Preliminary plans have been drawn for critical fish ladders for 

 Daguerre Point Dam on the Yuba River, and Sutter-Butte Dam on the 

 Feather River. Early construction of these fishways is of vital importance. 

 As the biennium ended, work was about to start on a series of small fish- 

 ways over several gravel dams on the Merced River. 



A large fish screen on Deer Creek was completely rebuilt, and a 

 by-pass was constructed. Work is about to start on the rehabilitation of 

 other screens and construction of by-passes on this stream and Mill Creek. 



Because it may be possible to substitute electric fish screens for 

 mechanical screens, and thus effect a great reduction in cost, we have 

 continued our experiments with these devices. In theory, electric screens 

 divert the migrating young salmon away from canal headings by shocking 

 them with a harmless but painful discharge of electricity. To date the 

 experiments have been disappointing. Some extensive changes in the 

 electrode system gave some promise when tried on a small scale, but failed 

 when applied to an entire screen. One difficulty has to do with getting the 

 young salmon far enough from the canal so that the current of the river 

 will take them on their way down the channel. Because most of the down- 

 stream migration takes place at night, and because young salmon are 

 attracted by light, it was decided to erect a series of moving lights to 

 attract the fish as they approached the screen. The lights would then lead 

 them downstream to a place of safety. The device, tried on a large screen, 

 has given definite promise; but biological, mechanical, and electrical 



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