Summer is here and with it comes warmer air temperatures and lower stream flows.

Grand County loses more water to trans-basin diversions across the Continental Divide than any other Colorado county. Already lower stream flows are exacerbated by these water diversions and consequently water temperatures increase more rapidly, too.

Trout require more oxygen than other fish, and when stream temperatures rise, the dissolved oxygen in the stream escapes into the atmosphere. The lack of oxygen in the water can send trout into a dormant state or even kill them.

Trout are very happy in water temperatures up to 65 degrees Fahrenheit. Temperatures from 65 to 68 degrees are when trout slow down and are susceptible to damage from catch-and-release anglers. Above 68 degrees the trout are seriously short of oxygen and catch and release is more likely to mean catch and kill.

At these higher stream temperatures, a trout will exhaust its oxygen supply fighting an angler’s line and can’t recover from that fight due to a lack of dissolved oxygen in the water. That trout will likely swim away only to die.

Savvy anglers fish with a thermometer and walk away when stream temperatures go over 68 degrees. During the warm summer months temperatures that threaten trout can be reached by noon on most days. To protect the future of our local trout fishery, anglers are asked to fish early and quit when stream temperatures are too high. The afternoon is a good time to go to a small stream at a higher elevation or to fish from lakes.

As afternoon stream temperatures have already reached 68 degrees on the Fraser River, and 70 on the Colorado River, it’s time to be kind to our cold water fishery and pay close attention to stream temperatures when fishing. If we do, we will have a healthy fishery for years to come.