Water Temperature and What It Means For Trout

Water Temperature and what It Means For Trout 

Temperatures in the south exceeded 90 degrees this weekend with the night time lows remaining above 70 degrees. These temperatures, in conjunction with low rainfall, can lead to rapidly rising water temperatures. This is a recipe for lethal water temperatures for trout. If you practice catch and release and continue fishing freestone rivers and streams when the water temperature gets too high, you run the risk of killing the trout you intended to safely release. If you are a catch and keep fisherman, you might be wasting your time as fish concentrate more on surviving than eating.

So what does water temperature mean when it relates to trout? Should you carry a stream thermometer? At what temperatures will the water be lethal to trout? I look to examine these questions in detail in this article.

Stream Thermometer

A stream thermometer is a very useful tool when it comes to fishing for trout. It could tell you where the fish are holding, how they are feeding and when you should probably switch from a freestone fishery to a tailwater fishery. Over the years, I have set up many packs and vests for trout fishing. When I began fishing I never thought I needed to know about water temperature or carry a thermometer. Now, I have one on every rig I own. It doesn’t matter if I am in a tailwater, a freestone headwater or a brook trout stream. They are fairly inexpensive and provide great value.

If you are fishing a stream that gets warm and forget your stream thermometer, get in an elevated position and watch the trout in the run. If they are holding in one place opening and closing their mouths, they are stressed. You may think they’re feeding, but they are not; they are trying to circulate more water around their gills to get more dissolved oxygen. It’s like they are gasping for air.

What Water Temperature Means to Trout

As water temperature rises, the amount of dissolved oxygen in the water decreases. Likewise, as the water temperature decreases, the amount of dissolved oxygen increases. This seems simple, right? But at what temperature should fishing be curbed to ensure trout survival? The actual temperature varies from species to species.


Brook Trout

Brook Trout need more oxygen (a lower water temperature) then rainbows or browns. This is why most brook trout streams are usually located at higher elevations. Studies vary on the overall lethal water temperature that will cause a Brook Trout to die. The optimal feeding temperatures for Brook Trout varies from 44 degrees to 64 degrees. The temperature that a Brook Trout begins to stress at is 65 and the water temperature at which could be lethal to Brook Trout is 70 degrees.

Cutthroat Trout

Ever wonder why there are very few Cutthroat Trout located in the South or why the Apache Cutthroat is so rare? It is because the only waters that can sustain a Cutthroat in the South is in the White Mountains of Arizona. Cutthroat’s optimal feeding and movement water temperatures are 39 to 59 degrees. When the water temperature hits 60 degrees, the Cutthroats will begin to stress and feed less. The lethal temperature for a Cutthroat Trout is 68.5 to 69 degrees.

Rainbow/Brown Trout

Rainbows and Browns are the more hardy of the trout family, which is why most states choose to stock them. The optimal feeding and movement water temperatures for them is 44 to 67 degrees. When the water temperature hits 68 degrees, both species will begin to get stressed. If the water temperature continues to rise and gets in the 75 to 77 degree range for an extended period, it can be lethal for Rainbow and Brown Trout. Studies have shown that if the water temperature goes up to 80 degrees, these two species can survive if the water temperature does not stay at these temperatures for longer than 24 to 48 hours.

When to curb fly fishing for Trout?

I know this is a lot of information to take in and that with all the different species that vary so much you might be wondering at what temperature should you stop fishing or switch to only fishing early in the morning before the water warms up during the day. Consider this. If there is a healthy population of wild Cutthroat and Brook Trout in a stream, then the water temperature will usually remain in that optimal levels.

Checking water temperature to try to protect the fisheries is really important in areas that: are seasonably warm during the summer, experience immense heat waves, or experience droughts. Where I live, we work very hard to improve the fishery and grow large trout; we watch the the water temperature constantly. When the water temperature hits 68 degrees, we will stop fishing for the Rainbows and Browns in the river and seek out tailwater/coldwater fisheries that are safe for the fish.

Even if you don’t release trout, have you ever noticed that later in the season the trout are not feeding as hard? When the water temperature hits 67 degrees, their feeding habits decrease significantly because the they’re conserving energy as their stress levels increase.

I hope this information helps educate all of our readers.
Good Luck on the Water
Joe with Soaring Eagle Outfitters