▁river ▁and ▁its ▁trib ut aries , ▁which ▁also ▁play ▁host ▁to ▁introduced ▁brown ▁tr out . ▁ ▁Pol l ution ▁For ▁its ▁size , ▁the ▁San ▁Jo aqu in ▁River ▁is ▁one ▁of ▁the ▁most ▁poll uted ▁rivers ▁in ▁the ▁United ▁States , ▁especially ▁in ▁its ▁lower ▁course . ▁Years ▁of ▁p estic ides ▁and ▁fert il izers ▁being ▁applied ▁to ▁the ▁surrounding ▁lands ▁as ▁well ▁as ▁municipal ▁run off ▁have ▁led ▁to ▁elev ated ▁levels ▁of ▁selenium , ▁flu or ide , ▁nit r ates ▁and ▁other ▁subst ances ▁in ▁the ▁river ▁and ▁its ▁trib ut aries ; ▁p estic ide ▁poll ution ▁is ▁now ▁considered ▁" ub iqu it ous " ▁to ▁the ▁San ▁Jo aqu in ▁River ▁system . ▁The ▁selenium ▁is ▁believed ▁to ▁origin ate ▁from ▁so ils ▁on ▁the ▁west ▁side ▁of ▁the ▁valley ▁and ▁in ▁the ▁Coast ▁R anges , ▁which ▁are ▁rich ▁with ▁the ▁element . ▁Additionally , ▁the ▁San ▁Jo aqu in ▁is ▁suffering ▁chron ic ▁sal inity ▁problems ▁due ▁to ▁high ▁levels ▁of ▁min er als ▁being ▁was hed ▁off ▁the ▁land ▁by ▁ir rig ation ▁practices . ▁Ab andon ed ▁mines ▁contribute ▁to xic ▁acid ▁mine ▁d rain age ▁to ▁some ▁trib ut aries ▁of ▁the ▁river . ▁One ▁of ▁the ▁worst ▁environmental ▁dis aster s ▁was ▁at ▁K est erson ▁Res er voir , ▁a ▁dispos al ▁site ▁for ▁agricult ural ▁d rain ▁water ▁which ▁double d ▁as ▁a ▁wild life ▁refuge . ▁Initial ly , ▁animals ▁and ▁plants ▁th riv