Trout & DROUGHT: Tips for Anglers

[Pat Stout]

The SRPG does not have any closure regulations for the Snake River, although it is a topic of much discussion. In recent years, the stream temperature can get up to 75-76 degrees Fahrenheit and has reached 80 F in past years. The annual stream temperatures have been quite good ever since dam releases were shut off for irrigation season. Of course, rain events, like the last couple of years and this year, can fill Merritt Reservoir and cause overflow of warm waters into the Morning Glory overflow valve by the dam. A large reason for the better stream temps is the diel temperature seen only with spring flows. The diel temp can range from 8-16 degrees F, so a temp of 74 F one day can drop 16 F to 58 F in the morning around 0800 hours. The maximum diel temperature is usually associated with lower night time temperatures in the 50s F. As a rule on the Snake River, the 1st 1.5 miles of stream are heavily influenced by the springs and dam seepage. By the time the flows hit the Stout reach, 82% of the stream temperature is influenced by ambient temperatures, rain, clouds and canyon topography (shade/trees/sun exposure). The springs are then but a minor component.

And here we are, drought and temps in the high 90s F breaking 100 F every so often. What can the angler do in these times? Some practical thoughts below.

Part of having no temperature regulations is predicated on the beneficial stream hydrology during the irrigation season and the spring flows. Secondly, fishery studies have also influenced our understanding of some streams, including the Snake River. Our own surveys also demonstrate a consistent and healthy trout population. See references below.

Reference: 2024 Fall Trout Survey

Reference: Idaho Fishery Study 

So, it is important to carry a thermometer AND USE IT. Once the stream reaches 69-70 F, it is time to consider retreating for a time. On the Snake River, the trout have acclimated to higher thermal tolerance, but 4-6 hours of 76F Waters does add stress. In fact, whether you release fish perfectly, some will die post release. Playing trout too long, too long out of the water, drying off in the sun and poor handling increase the stress and increase the likelihood that more trout will die. Barbless can help with a quicker release.

Time of day an angler fishes is often important. Fishing early morning or at the crack of dawn takes advantaged the cooler waters as mentioned regarding diel temperature change. Evening fishing is popular but not always advantageous due to the fact the lower half of the Snake River has  higher temperature during late afternoon or evening, sometimes at midnight. If interested, I can show a number of thermographs to demonstrate what happens on the stream.

Oxygen in the stream does not appear to be a particular problem. I have measured dissolved oxygen in 76F waters as high as 12. Most likely due to the many riffle/runs along the stream. In hot times, fishing in the riffle/run segments is a reasonable approach to find actively feeding trout. But as the stream temperature increase, that activity invariably decreases. A hint here, check the reach to see if the temperature is increasing or decreasing. If decreasing, there is a good chance of better fishing. I know some people fish areas of springs, but often they are low in oxygen despite a relatively uniform temp of 54-56F. Unless, the spring vent emanates well off the river and has time to flow through vegetation and sun (photosynthesis = O2).

Yes, I have added extraneous information to simulate the noggin. When out, remember 1.thermometer, 2.time of day, 3.Good catch & release technique, 4. Start paying attention to the stream and begin making mental notes about how flows, air temperatures, sunlight, and water temps all interact. Patterns emerge pretty quickly.

By the way, the trout are looking healthy and anglers are sending me some great pics!

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