Let’s Talk About Water Temperature. 7-12-20

In the world of rivers and trout fishing we are always talking about water temperature. We know the temperatures our favorite hatches come off, on the Rio the magic starting number for salmonflies seems to be 52°F with the hatch really getting rolling by 55°F. We know that a trout is very happy, eating and growing from 45°F-60°F. And lastly, we know when the water gets too hot 65°F+. Currently the Rio Grande has been reaching temperatures in the low 70’s by early afternoon, so we are asking people to hit the Rio early. Sunrise to 11AM has been our best window the last week or so, still fishing nymphs with a few small mayfly hatches going on.

So, 65°+ degree water temperature is too hot to trout fish, but let’s talk about why. Concentration of dissolved oxygen in water is directly affected by water temperature. Lower water temperatures can hold more dissolved oxygen than warmer temperatures, we have all heard of the “dead zones” in the Gulf of Mexico. These zones are caused by lack of dissolved oxygen due to high water temperatures. All vertebrate hearts need oxygen to survive, including fish. A study done on rainbow trout in 1977 by Kicenuik and Jones showed that a burst of exercise in the trout increased the oxygen needs of that fish by 400%. They correlated these oxygen demands with water temperature and determined that the trout would have catastrophic cardiac collapse due to depletion of oxygen reserves at certain water temperatures. At higher temperatures there just isn’t enough dissolved oxygen in the water to replace what is used during a fight with an angler.


Even if the Rio Grande is getting to hot to fish in the afternoons and evenings it is peak dry fly fishing on many of the smaller streams. Many of our local lakes and reservoirs are still fishing really well too. Give us a call or stop in for recommendations or to book a small stream fishing trip!