▁changes ▁in ▁water ▁properties ▁and ▁temper atures ▁on ▁either ▁side ▁of ▁the ▁bar rier . ▁A ▁difference ▁in ▁water ▁temperature ▁of ▁ 9 ▁degrees ▁Cel si us ▁was ▁once ▁measured ▁between ▁the ▁Columbia ▁and ▁its ▁trib ut ary ▁the ▁S nake ▁River . ▁When ▁s ilt ▁sett les ▁to ▁the ▁bottom ▁of ▁the ▁river ▁or ▁res er voir ▁it ▁covers ▁rocks , ▁ru ins ▁sp aw ning ▁grounds ▁and ▁elimin ates ▁all ▁hiding ▁place ▁for ▁smaller ▁fish ▁to ▁escape ▁from ▁pred ators . ▁Alter ation ▁in ▁water ▁quality , ▁such ▁as ▁acid ity ▁or ▁gas ▁s atur ation , ▁may ▁not ▁be ▁vis ually ▁dram atic , ▁but ▁can ▁be ▁dead ly ▁to ▁certain ▁types ▁of ▁aqu atic ▁life . ▁The ▁Columbia ▁River , ▁with ▁its ▁series ▁of ▁d ams ▁and ▁res er voir s , ▁is ▁influenced ▁by ▁a ▁complex ▁combination ▁of ▁these ▁effects , ▁making ▁it ▁difficult ▁to ▁predict ▁or ▁understand ▁exactly ▁how ▁the ▁animal ▁populations ▁will ▁react . ▁ ▁Sal mon ▁and ▁Ste el head ▁tr out ▁travel ▁from ▁the ▁ocean ▁up river ▁to ▁various ▁sp aw ning ▁grounds . ▁The ▁construction ▁of ▁multiple ▁d ams ▁on ▁the ▁Columbia ▁threatened ▁this ▁fish ery ▁as ▁the ▁fish ▁strugg led ▁to ▁complete ▁the ▁migration ▁up stream . ▁All ▁d ams ▁on ▁the ▁Columbia ▁River ▁down stream ▁of ▁Chief ▁Joseph ▁have ▁fish ▁l add ers ▁installed , ▁from ▁Well s ▁to ▁B onne ville ▁Dam . ▁ ▁M igration ▁down river ▁is ▁also ▁problem atic ▁after ▁d ams ▁are ▁built . ▁Pre -