Island Park Reservoir is a beautiful, 8,000-acre mountain reservoir in the heart of the Greater Yellowstone Ecosystem that contains once-productive fisheries for kokanee salmon, rainbow trout, cutthroat trout, brook trout, and mountain whitefish. These economically valuable fisheries have deteriorated due to high annual drawdowns in recent decades. Island Park Reservoir’s annual drawdowns are more extreme in drought years when water supply from winter snowpack is proportionally less than summer demand for irrigation downstream.

The RFHP funded crucial scientific projects which discovered that high drawdown increases Island Park Reservoir’s water temperatures and decreases dissolved oxygen concentrations. Hot surface water temperatures and a deep oxygen “dead zone” create a deadly habitat squeeze for Island Park Reservoir’s salmon and trout. The loss of habitat due to drawdown reduces fish populations in Island Park Reservoir.

Reducing the annual drawdown of Island Park Reservoir is a difficult proposition. Water from Island Park Reservoir helps irrigate one of the most valuable agricultural regions in the United States, the vast Snake River Plain, and farmers hold all rights to the water stored in the reservoir. Thankfully, with funding from the RFHP and with additional funding and partnership with the US Bureau of Reclamation, Idaho Department of Fish and Game, Fremont-Madison Irrigation District, and private landowners, the non-profit Henry’s Fork Foundation has implemented a huge collaborative water-saving program with two primary components: “Farms and Fish” and “Precision Water Management”. These programs work at scales from individual irrigators up to the entire 250,000-acre irrigation district to implement precision management projects based on increasing efficiency at the farm field level and managing water carefully at the district level, thereby reducing irrigation demand and overall Island Park Reservoir drawdown while simultaneously meeting on-farm goals. The Farms and Fish program has helped reduce annual Island Park Reservoir drawdown by nearly 20%, improving fish abundance by over 150% compared to years without water conservation.

Finally, detailed scientific information funded by the RFHP will support additional, durable measures to conserve fisheries resources for decades into the future. For example, scientific study on Island Park Reservoir discovered the conservation potential of complex infrastructure projects such as hypolimnetic oxygenation. Oxygenating the cold, deep “dead zone” in Island Park Reservoir could insulate fish habitat from drawdown and improve downstream water quality in the Henry’s Fork of the Snake River. Island Park Reservoir’s fisheries are in good hands because of RFHP funding.

Human Interest/Community Benefit:

Past, current, and future projects funded by the RFHP on Island Park Reservoir are win-win programs that benefit recreational and agricultural users alike. For recreational users, RFHP-funded programs are helping Island Park Reservoir and its tributaries meet management priorities defined by the Idaho Department of Fish and Game. These management priorities are restoring the fishery to its former status as well as reducing the impact of an increasing frequency of droughts that cause excessive drawdown. Island Park Reservoir and its main tributary, the Henrys Fork River, are popular recreational angling locations, especially for families, helping make the Henrys Fork the most popular fishery in Fremont County and supporting a local fishing-based economy worth around $30 million (Grunder et al. 2008, Loomis 2006). The fishery has declined since the 1980s when Idaho Department of Fish and Game (IDFG) data indicates it was a fishery of significant state interest and likely greater economic impact due to good catches of large rainbow trout (Oncorhynchus mykiss), cutthroat trout (Oncorhynchus clarkii spp.), and kokanee salmon (Oncorhynchus nerka) (High et al. 2015, Flinders et al. 2016). Funding from the RFHP has reduced drawdown even in extreme drought years, ensuring that Island Park Reservoir is well on its way to returning to its former status as a fishery of significant state interest.

The Farms and Fish program also benefits agricultural producers. Funding from the RFHP helped install Software Advisor Packages placed on center pivots with one or more farmers to apply irrigation water and maintain soil moisture for plant growth efficiently and uniformly. This software enhancement uses soil-water balance irrigation concepts and methods, along with crop growth models, as-applied irrigation data and hyper-local, field-specific weather data to generate the data needed to make more informed irrigation decisions. Initial estimates provided by center pivot irrigation manufactures clinical trials suggest a 25 to 50 acre-feet savings per center pivot. An obtainable goal of 5 center pivots in the Henry’s Fork Watershed would result in a possible 750 acre-feet savings in drawdown from Island Park Reservoir, while also improving efficiency and yields for agricultural producers. The Farms and Fish program upends the traditional adversarial relationship between agriculture and coldwater fisheries resources and replaces it with collaboration and cooperation with durable win-win solutions.

Partners:

• Utah State University Department of Watershed Science (USU)

• United States Geological Survey Cooperative Fish and Wildlife Research Unit (USGS CFWRU)

• Idaho Department of Fish and Game—Upper Snake Region (IDFG)

• Western Division of the American Fisheries Society (WDAFS)

• Idaho Department of Environmental Quality (IDEQ)

• US Bureau of Reclamation (USBOR)

• Fall River Rural Electric Cooperative (FRREC)

• Fremont-Madison Irrigation District (FMID)

• Private Landowners