oessiblo to salmon and steellioad 

 trout. Dams have been responsible 

 for this riMhiction of area availabh' 

 for 11 a t u r a 1 reproibict ion. The 

 liiiiuh-eds of sinall (hiiiis erected 

 many years a^'o in the C'obimbia 

 Basin in connection witii h)«:i:ino- 

 operations and for irrigation pnr- 

 [)oses (U'prived sahnon of headwater 

 spawnino- areas, as did Grand Con- 

 lee and other lar^e dams. Many 

 additional large dams are planned 

 for constrnction in the Colnmbia 

 River and these will fnrther limit 

 salmon migrations or make the re- 

 maining spawning areas more diffi- 

 cnlt to reach. Even if the adnlt 

 hsh surmonnt the dams and reach 

 the spawning gronnd, the seaward- 

 migrating fingerlings will snffer 

 heavy mortality in j)assage over the 

 dams and through the power tur- 

 bines. 



Another factor that has inijiaii-ed 

 the salmon resources is ])olbition 

 from in(histrial sources. In tlie 

 Willamette Rivei", tiibiitary to the 

 Columbia, a polhition block de- 

 stroyed the substantial chinook runs 

 not only by blocking the upstream 

 juigrations but also by causing the 

 death of any fingerlings migrating 

 downstream during the summer and 

 fall. Fortunately, very few streams 

 of the Pacific coast are so polluted as 

 to desti'oy runs entirely. Pollution 

 ^\■as one of the causes for the almost 

 complete loss of Atlantic salmon in 

 the New England States. Modern 

 regulations and laws have tended to 

 reduce this threat to salmon during 

 tiie relatively recent industrial de- 

 velopment of the West. In areas 

 liJve the Willamette River, where 

 pollution has actually blocked sal- 

 mon migration, substantial im- 

 pi ovement has been effected through 



I'^IOrKE 



-Fishways in fci 



uul and 

 ("oluinhi 



.n f: 

 Kiv( 



V shove at Bnnneville r>ii 



17 



