Given the changeable weather in Yellowstone in the spring, it’s not uncommon for the rivers and fish to get “shocked” by water temperature changes. I’ve written about this previously, in my article, Shocking the System. Here’s another example from the Madison River that took place last week.
Insect activity (and subsequent fish feeding) is regularly triggered by the water temperature moving off its low for the day. This fact is vitally important for anyone looking to time hatches and find the best fishing. For six days in a row, May 24-29, this temperature shift occurred mid-morning. Like clockwork, that’s exactly when flies hatched and fish rose. On May 30, the weather changed. Conditions were cold and wet, and it wasn’t until mid-afternoon that the water temperature moved off its low. That change in timing is clearly seen in the graph. Until then, no flies hatched, no fish rose. After the shift occurred, Pale Morning Duns and Baetis mayflies covered the water, with fish responding in kind.
Anglers attuned to the importance of water temperature and its effect on fly and fish knew there was no reason to rush to the river that day, unless they simply wanted to get cold, wet, and windblown (and then likely throw in the towel) before the fishing even began. This is one reason the best anglers I know pay attention to weather and water temperatures. They all carry stream thermometers, and use them daily. (Note that on any given day an emergence is never a guarantee, but if one is to take place it almost always follows this pattern.)
