▁high ▁flow ▁releases ▁sc our ▁gra vel ▁from ▁sp aw ning ▁b eds , ▁so ▁that ▁they ▁gradually ▁become ▁smaller ▁and ▁smaller . ▁The ▁smaller ▁pieces ▁of ▁gra vel ▁are ▁more ▁easily ▁picked ▁up ▁and ▁moved ▁down stream , ▁leaving ▁behind ▁larger ▁pieces ▁that ▁the ▁sal mon ▁are ▁unable ▁to ▁move ▁to ▁b ury ▁their ▁eggs ▁in ▁a ▁process ▁called ▁re dd ▁construction . ▁This ▁further ▁crow ds ▁the ▁sal mon ▁into ▁smaller ▁and ▁smaller ▁suitable ▁sp aw ning ▁b eds , ▁which ▁increases ▁the ▁lik elihood ▁of ▁re dd ▁super im position . ▁This ▁is ▁when ▁spawn ers ▁construct ▁their ▁re dd s , ▁or ▁po ckets ▁in ▁the ▁gra vel ▁to ▁lay ▁their ▁eggs ▁in , ▁on ▁top ▁of ▁pre ex isting ▁re dd s , ▁thereby ▁killing ▁or ▁b ury ing ▁some ▁of ▁the ▁eggs ▁in ▁the ▁pre - ex isting ▁re dd s . ▁▁ ▁The ▁E PA ▁has ▁also ▁stated ▁that ▁the ▁remaining ▁gra vel ▁is ▁" pro bably ▁fairly ▁highly ▁embedded ▁and ▁therefore ▁of ▁reduced ▁quality ▁and ▁un available ▁to ▁fish ▁for ▁sp aw ning ". ▁The ▁Tem per ature ▁of ▁the ▁water ▁can ▁also ▁affect ▁the ▁level ▁of ▁sp aw ning . ▁The ▁best ▁temper atures ▁for ▁spring ▁and ▁fall ▁run ▁Ch ino ok ▁sal mon ▁are ▁between ▁ 4 2   ° F ▁and ▁ 5 7   ° F . ▁However , ▁in ▁ 7 7 % ▁of ▁the ▁years ▁studied ▁by ▁the ▁San ▁Jo aqu in ▁River ▁Rest oration ▁Program , ▁water ▁temper