amento – San ▁Jo aqu in ▁River ▁D elta ▁near ▁M ok el um ne ▁City , ▁turning ▁west ▁once ▁more ▁to ▁join ▁the ▁M ok el um ne ▁on ▁the ▁border ▁of ▁Sac r amento ▁County ▁and ▁San ▁Jo aqu in ▁County . ▁ ▁River ▁modifications ▁ ▁As ▁one ▁of ▁the ▁last ▁rivers ▁flow ing ▁from ▁the ▁west ▁slope ▁of ▁the ▁Sierra ▁without ▁a ▁major ▁dam , ▁the ▁Cos umn es ▁is ▁a ▁vital ▁example ▁of ▁a ▁health y ▁waters hed . ▁However , ▁its ▁sal mon ▁and ▁steel head ▁populations ▁have ▁been ▁har med ▁by ▁invas ive ▁fish ▁species ▁and ▁poll ution ▁from ▁illegal ▁min ing ▁activity , ▁as ▁well ▁as ▁the ▁two ▁ir rig ation ▁di version ▁structures ▁near ▁Ran cho ▁M uri eta . ▁There ▁are ▁plans ▁to ▁re - int rodu ce ▁sal mon ▁sp aw ning ▁into ▁the ▁river . ▁ ▁Some ▁water ▁is ▁di vert ed ▁from ▁two ▁trib ut aries ▁of ▁the ▁North ▁F ork ▁– ▁Camp ▁Creek ▁and ▁S ly ▁Park ▁Creek ▁– ▁for ▁ir rig ation ▁in ▁the ▁Cam ino ▁area . ▁S ly ▁Park ▁Dam , ▁which ▁creates ▁ ▁J enk inson ▁Lake , ▁is ▁the ▁largest ▁water ▁storage ▁facility ▁in ▁the ▁Cos umn es ▁River ▁waters hed . ▁The ▁dam ▁and ▁res er voir ▁are ▁part ▁of ▁the ▁extensive ▁Central ▁Valley ▁Project . ▁However , ▁the ▁project ▁has ▁neg lig ible ▁effects ▁on ▁river ▁flows , ▁and ▁does ▁not ▁block ▁historic ▁sal mon ▁sp aw ning ▁runs . ▁ ▁D ams