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Idaho Fish and Game

Adult steelhead in the Potlatch River

If you rebuild steelhead habitat, the fish will follow


Although a long way from the Iowa farm where the Field of Dreams was built, the Potlatch River is home to the largest spawning area of wild steelhead in the lower Clearwater River basin. Currently, there are efforts underway to restore habitat and enhance the production of wild steelhead in the basin. For example, the removal of passage barriers, such as dams, roads and culverts can allow migratory steelhead to access upstream spawning and juvenile rearing habitats. 

One example of such a barrier was a 170-foot-long culvert on Big Meadow Creek, a tributary to the lower Potlatch River. Because of how the culvert was designed, flows were too low in the summer and too high in the spring to allow fish to move upstream. In fact, fish upstream of the culvert were thought to have been isolated since the early 1970s. In response, the Idaho Department of Fish and Game modified the culvert in 2018 by installing baffles along the bottom. This slowed flows in the spring and retained water in the summer making it possible for steelhead to access an additional 10 miles of stream habitat!


Highway 8 Culvert
A picture of the culvert on Big Meadow Creek before and after the installation of baffles designed to make upstream passage easier.

To evaluate the ‘success’ of this project, fisheries biologists sampled the upstream section before and after culvert modification and collected genetic samples. The expectation was that if the culvert was no longer a barrier, anadromous adults would be able to spawn upstream of the culvert. From the juvenile fish that were sampled, we would expect that their genetic composition would become more similar to steelhead and not resident Rainbow Trout.

Lo and behold, a rapid shift in genetic composition was observed. In 2018, upstream fish shared little genetic similarity to local steelhead. But two years after restoration, the upstream population was nearly identical to steelhead from nearby streams. This project, along with many others, aim to increase the production and resilience of steelhead populations in the Potlatch River for generations to come!

Diagram of shifting genetic composition of steelhead
A map showing the shift in genetics through time. Dark circles are genetically more similar to steelhead and light colors represent resident trout.