Reduced Winter Flows… Why you should be concerned!

The Shoshone River is a blue ribbon trout river which flows from the slopes of the Yellowstone Caldera, eastward through Cody, Wyoming, to join with renowned fly fishing mecca, the Big Horn River.

But, its journey is perilous.

In addition to impacting trout health, reduced winter flows expose the river bed to freezing temperatures and dehydration in turn, damaging critical aquatic habitat.
Shoshone River 12.19.2020 KC

Winter Flows and Impact to Trout on the Shoshone River

East Yellowstone TU members are concerned about a confluence of events that may result in harmful impacts to the wild trout population in the Shoshone River below Buffalo Bill Dam. The first event was the decision to reduce winter flows in the Shoshone River to 200 cubic feet per second (cfs). The decision is based on the 10 year Winter Release Operating Agreement approved in 2019. Under the criteria in the agreement, if the reservoir level is below 475,000 acre feet on October 1, and the Wyoming State Account is greater than 95,000 acre feet, the winter release is 200 cfs. As of October 1, reservoir levels were at 437,000 acre feet so the flows were reduced to 200 cfs.
The second event is population sampling conducted by Wyoming Game and Fish for the river reach above Belfry Bridge. The sampling estimates a population of over 8,000 fish per mile! So fish populations are at an all-time high while flows and habitat are reduced.

The third event relates to water temperature and impacts to trout metabolism. With the decreased flows, the impacts of DeMaris hot springs on water temperature is more pronounced. Water temperature data was collected at Belfry Bridge over the past several weeks: On Dec 8 the water temperature was 49.1 degrees F on Dec 12, 47.3, on Dec 20, 46.4 on Dec 27, 46.4 on Jan 6, 46.4 on Jan 14, 43.7 and on Jan 20, 44.6.

If you consider water temperature influence on trout metabolism, the current water temperatures are favorable for trout metabolism. However, with the reduced flows and loss of habitat due to exposed riffles and banks, food sources to support the high number of trout are likely to be inadequate, resulting in a loss of condition. EYTU members will continue to monitor temperatures and fish condition.

The 2003 WY Game & Fish study titled “WINTER FLOW RECOMMENDATIONS FOR THE SHOSHONE RIVER BELOW BUFFALO BILL DAM” provides the best science for optimal winter flows for trout. Vogt and Annear (1991) determined that 350 cfs at the Buffalo Bill Power Plant, as stipulated in the Annual Operating Agreement, would maintain the Shoshone River tailwater blue ribbon fishery. Due to accrual from DeMaris Springs, 350 cfs at Buffalo Bill Power Plant translates to about 410 cfs at the USGS gage assuming 60 cfs of spring contribution (Vogt and Annear 1991). 

Therefore, the 440 cfs recommendation resulting from our intensive work is only 30 cfs (7.3%) higher than the results from the original instream flow analysis. Specifically, a flow of 440 cfs was identified through the PHABSIM incremental analysis and supported by analysis of the other important riverine components. Under PHABSIM, 440 cfs would maintain a peak level of both brown and cutthroat trout habitat indices. Lower flows would maintain a cutthroat trout habitat index down to 340 cfs but the brown trout habitat index would decline.

Higher flows would maintain relatively high levels of habitat but are not necessary for maintaining habitat. Based on hydrologic analyses, 440 cfs is approximately the same as the average winter flow of 444 cfs during the 1973-2002 period. Therefore, 440 cfs seems a reasonable quantity that has been demonstrably achieved during recent years.

Next Steps

EYTU will continue to work with agencies to modify the 2019 Winter Release Operation Agreement to provide for more favorable winter flows for trout. EYTU members met with Bureau of Reclamation staff on November 19 to discuss dam operations including the winter flow agreement. Any changes to the flow this year will require modification of the agreement which is not likely this year.
The current Winter Use Operating Agreement was approved in 2019 for a 10 year term. A categorical exclusion (CE) under NEPA was completed. (We will seek a copy of the CE. Generally CE’s are appropriate if there are no significant environmental impacts and there is little to no public interest or controversy. Arguably, environmental impacts of low flows are significant to aquatic habitat and aquatic life. And public involvement for the CE was likely minimal even though there is a great deal of interest in the Cody area).
Signatories include: Area Manager, BOR Director, Wyoming Water Development Office WY Attorney Generals Office WY State Engineers Office Director, WY Game and Fish Governor, State of WY

What you can do

 
When fishing over the winter months, play and release fish quickly, keeping them in the water if possible Report any fish kills or diseased fish to EYTU officers: President Tom Brown or Vice President Larry Timchak at president@eastyelowstonetu.org . 

Contact Tom or Larry if you have any questions about the winter flows and the Winter Flow Agreement.