Madison River Dam Update

Written by Pro Staff Mike Lum based in Southwest Montana,

Pictures by Joe Dilschneider from the Madison River Fishing Company

At around 2 a.m. on November 30th 2021, a piece of newly installed equipment within the structure of Hebgen Dam on the upper Madison River in SW Montana failed, causing dam intake gates to slam shut, dropping the outflow flow from around 650 cfs to just under 280 cfs in about 15 minutes. Over the course of the next 24 hours the flow continued to drop to around 215 cfs. It took the owner of the dam; Northwestern Energy, just under 48 hours to become aware of, vet and fix the problem, restoring normal flow to the river. This certainly could have been a catastrophic event for one of the west’s and indeed, flyfishing’s most iconic waters. The jury is still out on possible long-term ramifications but river characteristics and circumstances, in particular weather, may have provided some buffer to any real catastrophe. 

For those not familiar with the Madison, it’s a relatively shallow river beginning within the confines of Yellowstone National Park, flowing outside the park borders, it enters Hebgen Lake (technically Reservoir). It then progresses downstream for about 2 miles where it dumps into Earthquake Lake. The river then flows over the top of the earthen dam (formed by, unsurprisingly, an earthquake in 1959) and downstream towards the town of Ennis, a journey of about 46 miles. These details are important to understanding what may end up being mitigating factors to this narrowly avoided disaster. 

What makes the Madison unique is, among other things, the mitigating effect of Quake Lake on downstream flow changes. When flow changes are initiated at Hebgen dam it takes several hours for that change to be reflected in the river directly below Quake Lake and almost 24 hours for that flow change to reach the town of Ennis. The 2 mile stretch of river between the lakes would see a much more dramatic and fast flow change and therefore any redds there may have been more critically affected. This remains to be seen.  
Another mitigating factor for larger fish downstream of Quake is their sensitivity to flow change and ability to move to deeper water. This bore out as rescue volunteers witnessed very few catchable sized fish stranded in dewatered side channels other than between the lakes and in some cases directly below Quake. There did seem to be higher numbers of smaller, young of the year fish stranded in some of these spots but even those fish, with adequate time, seemed to be able to move to deeper water as evidenced by fewer to none stranded in the lower stretches. 

What may prove to be the biggest saving grace came from Mother Nature. As difficult as it is to believe, night time air temperatures on December 1st did not drop below freezing in the Madison Valley. Had they done so, we could be sure that all those eggs exposed by the lowered flow would have frozen. Instead, even redds which were dewatered may have stayed wet enough and were exposed for a short enough period of time that in all likelihood the eggs remained viable. 

In the end, the Madison River, her trout and everyone who loves this world class fishery may have just dodged an enormous bullet. Time will tell. If we lost some young of the year or viable eggs from those redds it will take 2-3 years before it really becomes noticeable and Mother Nature has ways of compensating for any “holes” in ecosystems. It’s even possible we end up with a greater percentage of larger fish for a few years. 

Northwestern Energy is currently bearing the brunt of outrage over this incident, as well they should. FERC, the government agency which licenses and oversees dam structures and management in the US will hold NWE accountable and there are several formal complaints filed by 3rd party interests. Changes will be made to practices and technology to make instances like this less dramatic and ideally less impactful. 

On another, potentially more critical note for the long-term health of the Madison as well as every other river in the state, we are currently experiencing a 2nd year of dramatic drought conditions here in SW Montana. Water management and resource conservation should and will be front of mind for all of us here in the near and long terms. Stay tuned!

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