Why Water Temps Matter: Summer Fly Fishing with Care

As summer heat settles in across Colorado, our rivers begin to feel the effects—often faster than many anglers realize. Rising air temperatures lead to rising water temps, and that can put trout under serious stress. Warm water holds less dissolved oxygen, which makes it harder for fish to recover after being caught. For anglers practicing catch-and-release, this means we need to be extra mindful of how and when we fish.

One of the best ways to protect the fishery is by checking water temperature throughout the day. It’s simple to do with a digital stream thermometer, we like the Fishpond Riverkeeper Digital Thermometer. Clip it to your boot laces and let it sit fully submerged in the current for about 30–60 seconds or -even better- leave it there all day to check periodically. You’ll get a more accurate reading than if you dip and pull it out quickly. Leaving it on your boot also gets the reading from the most important part of the river column, as the bottom and surface of rivers will be different temperatures. Start checking temps by late morning, and again in the early afternoon when rivers are at their warmest.

As a general rule, consider wrapping up your river fishing once the water approaches 68°F (see chart at bottom of blog). At that point, even a quick fight on light tippet can be dangerous for a trout. Instead, plan your day around cooler windows. Early morning hours—especially before 10 a.m.—are typically best. If you’re still itching to fish later in the day, wait for the sun to drop and target evening hatches. The drop in temps and increased insect activity can make for some of the best dry fly fishing of the season.

Stillwater options like lakes, reservoirs, and alpine ponds are also great alternatives during hot spells. Deeper water tends to stay cooler, and trout often remain more active even in the middle of the day. Many of our local stillwaters are fishing exceptionally well this time of year and offer a change of pace and scenery – and a chance to escape the river crowds.

Paying attention to water temperatures isn’t just about improving your success—it’s about ensuring the health of our fisheries for the long haul. As anglers, we’re stewards of the resource. Let’s fish smart, stay cool, and protect what we love!