Native populations of Yellowstone cutthroat trout are to benefit next week when the US Bureau of Reclamation’s Pacific Northwest branch increases flows from the Palisades dam.

Beginning on 17 May, engineers are to raise flows from an initial 310m3/sec up to a maximum of around 510m3/sec, a figure which will be maintained for about three days. The action is to be taken following the completion last year of a fishery statistical analysis, which was carried out to determine the relationship between flows and fish numbers, as well as the timing and size of flow regimes that would favour the cutthroat fish population over the non-native rainbow trout.

The work found that the cutthroat would benefit most from steady flows from the dam during the winter season followed by much larger spring peak discharge. The operation is expected to cause river levels to rise by around 0.6m from 18–23 May. Flows will then be reduced to summer irrigation levels.

The work is aided by increased storage in the Palisades reservoir, a result of relatively low flows from the dam last winter.