The man-made Delta Cross Channel transports fresh water from the Sacramento River into the interior of the Sacramento-San Joaquin Delta.
The channel is about 30 miles south of Sacramento near Walnut Grove. That fresh water is eventually pumped south to provide drinking water to 25 million Californians.
But with the gates open salmon can be confused and be diverted from their migratory path up the Sacramento River. The National Marine Fisheries Service requires their closure.
The gates will close Monday morning and remain closed until further notice. Boaters are also advised to check the status of the gates.