Two years after the last of the four lower Klamath dams came down, USGS is checking whether its own predictions held up. In an August 4 status update, the agency’s Western Fisheries Research Center described a five-year study of how juvenile chinook, coho, and steelhead are moving through the reopened river. The point is to compare the actual migration data against the pre-removal models.
Those models predicted that pulling J.C. Boyle, Copco No. 1, Copco No. 2, and Iron Gate would warm the water earlier in spring, keep it cooler through midsummer, and shift the flows that determine how many young salmon reach the ocean. The release puts it plainly: “our staff are determining if the predictions were correct.” The four dams were built between 1918 and 1962. Demolition ran from 2023 through 2024, opening more than 400 stream miles to salmon and steelhead, including cold-water tributaries in the upper Klamath Basin.
They’re testing these predictions in two ways. USGS scientists surgically implant acoustic tags in juvenile salmon and track them with eight listening stations along the river as the fish move downstream. California Department of Fish and Wildlife catches out-migrating juveniles in rotary screw traps below where Iron Gate once stood, marks them, releases them upstream, and counts how many come back through. Between the two, USGS gets migration timing, route, and survival numbers to line up against what the model predicted.
WFRC scientists also think cooler water, more natural flows, and expanded side-channel habitat could slow migration, give fish more time to grow before they head out, and produce a more varied mix of outmigrants that over time could feed the portfolio effect that stabilizes salmon populations. Those are hypotheses, not findings. The release doesn’t report any results.
The eventual findings will feed flow-management decisions on the river, and Klamath fly anglers have a stake in those calls. In June, MidCurrent covered CalTrout and The Conservation Angler launching an angler-science partnership on the river. George Pess, a 26-year NOAA veteran now with TCA, said anglers are “among the first people to notice when something changes on a river.” The fall chinook fishery opens August 15 and runs through December 31, and half-pounders and summer-run steelhead are already in the system. USGS has three more years of data collection to run.
