One of the most important factors in a trout’s environment is cold, clean water. Trout thrive in Colorado because they LOVE cold water. Even at our elevation, though, most of our streams, lakes, and rivers can be negatively affected by higher water temperature.
With the direct overhead summer sun and longer days, our waters warm up quickly. It does not take long for the median water temperature to reach dangerous levels that can threaten a fish’s health. Even though we had a wet winter and recent rainy afternoons, it doesn’t mean that we won’t be seeing higher water temps as we move through July and into August. In fact, we are seeing water temperatures getting higher through Cheesman Canyon and Deckers because of the warmer water spilling from Cheesman Reservoir. When water is released from the valves lower in the dam, water temps will drop.
Optimal water temperature for trout is about 40 to 65 degrees, plus or minus a few degrees on each side. On the high side of these temperatures, trout can easily become stressed and lethargic. When trout are caught in high water temperatures, the mortality rate is extreme. Even if the angler properly handles and releases the fish, the chances are very high that the fish will not survive.
Most fishermen I know have an unspoken rule that when the water temperature reaches 68 degrees, it’s time to go home.
All of our fisheries are susceptible to reaching these higher temperatures. Some conditions – such as flows levels and currents – will impact the water temps, for sure. But fish thrive in cold water. When water temps rise, oxygen decreases, food sources are impacted, fish are more susceptible to disease and illness, and they tire more quickly under the strain of the fight. A fish’s metabolism changes along with temps (think of how sluggish fish are in the winter months). Those changes as the water warms and water temps reach 70 degrees over a long stretches of days are life threatening.
A good way to combat the adverse effects of the heat in the summer is to fish either in the morning or the evening. The water temperature will be highest in the middle of the day.
Where you fish is important, too. Trout will move into more oxygenated areas in the river when temps are high to seek relief. Riffles, deeper runs, rapids, etc. tend to hold cooler water and more oxygen. Dissolved oxygen refers to the amount of oxygen in the water – and rainbow and brown trout thrive on higher levels of dissolved oxygen. Warm water lowers dissolved oxygen amounts. In addition, the higher than normal aquatic vegetation reduces water velocity – which further impacts both oxygen levels and bug life.
A good tool to have on the river is a thermometer and one of our guides’ favorite is the Fishpond Swift Current Stream Thermometer.
To be good stewards of our limited resources, some effective summer habits include
- Fish earlier in the day and maybe even call it a day at noon.
- Fish some of our stillwaters from the shore, from a belly boat, or maybe book one of our guided kayak fly fishing trips.
- Buy a thermometer (follow the link to our online store or come on in to the shop!) as your next gadget and check the temps.