Eastern Idaho Water Rights Coalition Members:

For 17 years “flow augmentation” water has been released from Idaho reservoirs to aid in salmon and steelhead migration to the ocean.  This includes water from our Upper Snake Reservoirs.  This year the amount of water sent downstream from Upper Snake River storages – not natural flow – was roughly double the shortage of the Twin Falls Canal, which led to the massive curtailment order last spring.

The information below, provided by the Idaho Water Users Association, summarizes an Idaho Department of Fish and Game study on the impacts of the flow augmentation.

Flow Aug & Salmon Survival: Over the last year or so, the Idaho Department of Fish & Game has analyzed flow augmentation and its impacts on survival of out-migrating salmon and steelhead.  The Fish Passage Center recently released a draft 2024 Comparative Survival Study that discussed this F&G analysis.  You can review this discussion in Chapter 7 of the report (pdf page 256).  The report concludes:

We used vastly improved fish detection datasets and survival models to demonstrate that the flow augmentation program as implemented over the past 17 years did not yield appreciable benefits to anadromous fishes in the Snake River basin. Our analysis evaluated the outcome of a long-standing management action as required for adaptive management and begins to address a state’s policy recommendation within the scope of the CSS project. 

We do not attribute this result to a lack of flow/survival relationship as suggested in the past because the strength of that relationship is implicit in the model framework included in Chapter 3 of this report. The complexity of moving water across the landscape and water accounting associated with established laws and agreements hinder the ability to place water at times and places (i.e., shaping) most beneficial to anadromous fishes. In a given year, water can be released to coincide with peak flow, in which case its contribution to total flow, survival, and travel time is low. Alternatively, water can be released when flows are lower, but fewer fish are present to potentially benefit. Attempts to find a middle ground will lead to water being spread out over time to ensure that realized benefits to anadromous fishes are negligible. Our analysis underscores the difficulty of using water as the sole management action to decrease water transit time and increase fish survival in the lower Snake River.