47 



Estimates of the historical runs indicate that from 10 to 

 14 million adult salmon and steelhead entered the Columbia River 

 each year. The current run size is approximately 2.5 million. 

 Salmon and steelhead habitat in the Columbia River basin above 

 Bonneville Dam has decreased from about 11,700 river miles before 

 1850 to about 7,600 miles today, a 35 percent reduction. Much of 

 the reduction in the numbers of anadromous fish can be attributed 

 to blocked access to habitat resulting from hydropower dams and 

 passage losses associated with the dams. Other factors, however, 

 were also at work. 



Irrigation and flood control, as well as poor logging, grazing, 

 and farming practices resulted in depleted streamflows, erosion, 

 loss of riparian habitat, and a general degradation of much of 

 the remaining habitat. Between 1936 and 1942, more than 5,000 

 miles of tributaries to the Columbia River were inventoried by 

 the U.S. Bureau of Commercial Fisheries (now NMFS) for pool and 

 substrate characteristics. These surveys were done in relatively 

 undisturbed watersheds to document stream habitat conditions for 

 anadromous fish before additional dams were built on the Columbia 

 and Snake Rivers. A recent comparison of these data with current 

 surveys shows that river systems impacted by human activities on 

 public and private lands have lost 50 to 7 5 percent of their 

 large pools during the past 50 years. Large pools are critically 

 important for anadromous salmonids, functioning as resting areas 



