ed ▁in ▁the ▁artificial ▁wet lands ▁that ▁were ▁created ▁here , ▁but ▁in ▁ 1 9 8 3 , ▁it ▁was ▁found ▁that ▁birds ▁had ▁suffered ▁severe ▁de form ities ▁and ▁death s ▁due ▁to ▁stead ily ▁increasing ▁levels ▁of ▁chemical s ▁and ▁to x ins . ▁In ▁the ▁next ▁few ▁years , ▁all ▁the ▁fish ▁species ▁died ▁except ▁for ▁the ▁mos qu ito ▁fish , ▁and ▁alg ae ▁blo oms ▁pro l ifer ated ▁in ▁the ▁f oul ▁water . ▁These ▁have ▁had ▁not ▁only ▁an ▁ad verse ▁impact ▁on ▁San ▁Jo aqu in ▁River ▁e col ogy , ▁but ▁also ▁cause ▁poll ution ▁to ▁the ▁sources ▁of ▁most ▁of ▁the ▁large ▁aqu ed uct s ▁in ▁the ▁state ▁– ▁the ▁California ▁and ▁D elta - M end ota ▁Can als , ▁for ▁example . ▁ ▁Sal mon ▁Before ▁ir rig ation ▁development , ▁the ▁San ▁Jo aqu in ▁River ▁and ▁its ▁trib ut aries ▁once ▁supported ▁the ▁third ▁largest ▁run ▁of ▁Pacific ▁sal mon ▁in ▁California ▁including ▁pro dig ious ▁spring , ▁summer , ▁fall , ▁and ▁late - fall ▁runs ▁of ▁ch ino ok ▁sal mon . ▁The ▁California ▁Department ▁of ▁Fish ▁and ▁Game ▁estimated ▁in ▁the ▁ 1 9 3 0 s ▁that ▁the ▁historic ▁sal mon ▁run ▁was ▁likely ▁in ▁the ▁vic inity ▁of ▁ 2 0 0 , 0 0 0 ▁to ▁ 5 0 0 , 0 0 0 ▁of ▁spawn ers ▁ann ually , ▁but ▁by ▁the ▁mid - 2 0 th ▁century , ▁reduction