A number of small tributaries drain directly into the South Fork Boise River, but their contribution for spawning and rearing habitat is poorly understood. Potential tributary enhancement projects could be effective, but the first step is learning whether fish are presently using the tributaries and the water conditions, whether the culverts inhibit or prevent fish passage, and habitat present in those tributaries.
The Boise National Forest has identified the culverts on four South Fork tributaries as barriers to Aquatic Organism Passage, typically referring to fish but can be other biologically important species. Culverts installed typically prior to the 1990’s like those on the SFB tributaries, are not designed for fish passage since they typically move water faster than the stream itself. While fish swim against a current at higher speed in shallow water, their passage through the culvert when moving upstream from the river to the tributary can be restricted due to water velocity, length of the culvert and depth of water.
