Environmental History 
of the Spokane River


March 29, 2016

In 2016, Avista planned a construction project at the Long Lake Dam to help reduce potentially harmful oxygen levels. The dam leads to a 200-foot spillway and when water plunges over, it becomes saturated with oxygen and/or nitrogen. That saturated water could be harmful to fish further downstream where testing indicates that the oxygen levels downstream exceeds the state standard. To address this, Avista installed deflectors above the spillway which will change the flow from plunging, to more of a horizontal flow which should help reduce the oxygen levels in the water that goes over a dam.

December 1, 2017

In April through December of 2016, Avista completed an $11 million construction project at Long Lake Dam where the water showed elevated levels of air dissolved in the river. Avista decided to install deflectors on the lower face of the dam to make the water skim instead of plunge at the dam’s base. It also reduced the depth of the dam’s plunge pool and removed rock at a nearby outcropping so it would not obstruct the flow of the river. These changes should lower dissolved gas levels in the water and keep the fish healthy. In March through June, Avista began monitoring dissolved gas levels in the water to test how well the deflectors work with initial results indicating the modifications have helped to reduce dissolved gas levels downstream of the dam.

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