What Water Temperature Means to Trout
Checking water temperature to try to protect the fisheries is really important in areas that: (1) are seasonably warm during the summer, (2) experience immense heat waves, or (3) experience droughts.
Warmer water contains less oxygen than colder water. As temperatures rise and dissolved oxygen decreases, fish begin to experience stress. These stresses begin to set in well before the water temperature reaches lethal limits.
But at what temperature should fishing be curbed to ensure trout survival? The actual temperature varies from species to species but brown, rainbow and brook trout begin to experience some level of stress at around 68°F, with that stress increasing rapidly as the temperature rises further. A safe rule of thumb is that 70°F represents the "don't fish" limit.
When the water temperature hits 67 degrees, their feeding habits decrease significantly. The problem isn't the water temperature as such. It's the low oxygen levels associated with the warm water and because the they’re conserving energy as their stress levels increase.
Catch and release fisherman should pay specific attention to stream temperatures. A stream thermometer is a very useful – and inexpensive - tool to carry that can help you out. Just use common sense and take care of the fish.
Sources: theperfectflystore.com; hatchmag.com; troutsflyfishing.com