How these numbers are made. Steelhead carrying PIT tags are detected at dams and
in-river antennas; each tagged fish is expanded by its group's published tagging rate to
estimate untagged fish traveling with it. Levels are anchored to the Bonneville census
and cross-checked against independent published sources (IDFG/ODFW run reconstructions,
dam-by-dam census bounds). Status timing for this river reads the Prosser count.
These are
estimates — treat year-to-year shape as more reliable than any single
year's absolute level. Full methodology on the
dashboard About tab.