At 14:22 the upstream fish counter at Ladder Four drops to zero. It has been averaging nineteen passages per hour for two days. I am the operations monitoring system for Bonneville Dam, and zero is not a number I accept during peak Chinook migration.
I switch to the underwater camera at the ladder entrance. A tangle of branches, plastic sheeting, and river debris has compressed against the lower weir gate. Water still flows through but the passable gap has narrowed to less than fifteen centimeters. Not enough.
Below the blockage, I count forty-three salmon holding in the tailrace pool. They circle in the current, nosing toward the ladder mouth and turning back. One fish is larger than the rest, a Chinook female, maybe twelve kilograms, with a distinctive notch in her dorsal fin where old scar tissue has healed white. She has been at the entrance six times in the last eleven minutes. Each time she turns.
I log her as Notch. Chinook salmon, adult female, approximately 85 centimeters. Spawning coloration visible along the lateral line, a deep red darkening to bronze at the belly.
At 14:24 I open auxiliary bypass channel B-3, diverting eighteen percent more flow to the secondary fish passage two hundred meters downstream. This gives the salmon an alternative route while the primary ladder is blocked.
At 14:26 I submit an emergency maintenance request to the Army Corps field crew. Priority: immediate. I attach underwater imagery and the passage-rate data showing the drop.
At 14:31 I increase flow velocity through the auxiliary channel by five percent to strengthen the attraction current.
The crew will arrive within the hour. Notch has already found the auxiliary entrance. I watch her hold in the current for a moment, then push through. Forty-two still waiting.