An estimated 2,240 juvenile salmon and steelhead were found dead on Wednesday at Little Goose Dam near Starbuck.
The abnormally high amount of wood and other debris floating down the Snake River this spring plugged an opening at the juvenile bypass system. The system has 36 opening to attract juvenile fish from a collection channel with lights.
The Army Corps will increase monitoring of openings to every two hours around the clock.
Last month nearly 100 juvenile salmon and steelhead died at the Little Goose Dam when a fish separator system at the Juvenile Fish Facility became plugged with debris and it overflowed.
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Millions of fish migrate downstream this time of year at Little Goose.