As the summer approaches I’m always thinking about how the warmer temperatures will affect trout fishing. Rainbow trout are active in water temperatures around 59 degrees and like highly oxygenated water. But what happens as the water becomes warmer as day/night temperatures rise? In Southern California the shallow lakes cannot support trout because the water temperature is too warm. Here’s some trout info on temps and oxygen:
- Mortality temperature is 75+ degrees for trout
- Trout farms recommend having dissolved oxygen (DO) higher than 5-7 mg/l
- Mortality DO is less than 2 mg/l
- Water will maintain DO above 8 mg/l at 75 degrees
- DO at 75 is above 8 mg/l
Yeah, my friend the Ichthyologist, Big D will find the scientific studies interesting. But I believed trout always sought out highly oxygenated water during the summer. I learned that warm water can hold more than enough of oxygen for them. So, I dug some more and found a link (below) for an interesting study where they monitored trout behavior in a confined natural pool. The pool had areas with cool water with little oxygen (2 mg/l) from underground aquifers or warm (70+ degree) highly oxygenated water near the surface.
- During the day, the trout grouped around the cool water aquifer that had borderline mortally low oxygen levels
- During the night, the trout spread out a little to warmer water with higher oxygen levels
So, Mr. Trout is temperature sensitive above all. No wonder it’s hard to catch trout in the warm summer months. But it explains why I’ve had great trout fishing in the evening and or cold mornings, while it’s totally dead in the heat of the day. I’m going play like Mr. Trout as the weather gets hot in summer. Fish during the early morning and evening. Then go to a nice cool spot during the heat of the day (that serves beer). Like I’ve always thought – Mr. Trout is pretty smart.