"This persistent heat dome over the West Coast will likely result in earlier loss of ability to provide cool water and subsequently, it is possible that all in-river juveniles will not survive this season," CDFW said in a statement.

California, among other Western states including Oregon and Washington, has been experiencing extremely high temperatures in recent weeks. But drought conditions in the Golden State are especially taxing, with much of the state under severe or exceptional drought, according to the U.S. Drought Monitor.