INTRODUCTION 



Demands for additional water supplies for irrigation and pro- 

 duction of hydroelectric power in the Central Valley and adjacent areas 

 in California, focused attention on the upper Trinity River drainage as 

 a possible source of supply. Plans to divert Trinity River water into 

 Sacramento Valley from that area were formulated and published in 1931 

 as a part of the California State Water Plan. These plans were further 

 studied and refined by the tJ. S. Bureau of Reclamation and U. S. Army 

 Corps of Engineers and by 1941, their realization seemed certain. It 

 was also apparent that diversion of Trinity River water would seriously 

 affect the fishery resources that are dependent upon the upper river^ 

 particularly king salmon and steelhead trout. In order to determine 

 the magnitude and biological characteristics of these resources and to 

 design management plane and procedures for their protection, the U. S. 

 Fish and Wildlife Service conducted a comprehensive survey and study of 

 the entire problem. Major features of the study involved determination 

 of: (1) the size and composition of fish population, (2) the character- 

 istics of the seaward migration of young salmon and steelhead trout, 

 (3) the extent and utilization of spawning gravels, (4) the physical 

 characteristics of the drainage, (5) existing biological conditions, and 

 (6) possible means of controlling the fishery and its environmental factors* 



Work was first started in the fall of 1942 when a temporary fish 

 counting weir was constructed on the Trinity River a few hundred yards 

 below the river bridge at Lewis ton (see map) and approximately 105 miles 

 upstream from the river's mouth. Studies of some of the biological and 

 physical conditions of the streem were also started during November of 

 1942. The temporary fish counting weir was replaced with a removable 

 structure in late 1943. Because of wartime impediments, uninterrupted 

 studies of the Trinity River fishery covered a period of only two years* 

 As a result, it is impossible to make positive and final conclusions* 

 This report, therefore, is an interim report with most findings and con- 

 clusions subject to possible revision pending further investigational 

 findings. 



Trinity River, largest of the Klamath River tributaries, rises 

 in the Scott Mountains at the northern end of Trinity County, California* 

 It courses south and west through Trinity County, then north to its con- 

 fluence with the Klamath River in Humboldt County. The less canyonous 

 portions of the river bed abound with broad gravel riffles and provide 

 excellent spawning grounds for king salmon. Numerous small tributaries 

 and the upper part of the main stream furnish adequate spawning ground 

 for large numbers of anadromous and resident trout* Like many of the 

 rivers in the northern California, its run-off pattern consists of extremes 

 in flood and in drought. During STimmer, its flow is extremely low. In 

 winter and spring, it rages destructively when in flood and discharges 

 much of its annual run-off. 



