We get asked a lot of questions and one of the most common one’s we receive is, “what is an ideal flow for this river, right now?” While it’s a relatively easy question to answer based on every river having a unique flow range that is deemed “ideal”, it’s not necessarily straightforward during the spring and early summer due to runoff. Daily fluctuations in flow are common and even though flows may be in the prescribed “ideal range”, it doesn’t necessarily mean that they are good, right now. This leads us to our point that not all flows are created equal.

So, what do I mean when I say that not all flows are created equal? To put it simply, 1,500 cfs on the Middle Colorado River in May won’t necessarily fish the same as 1,500 cfs in August. Yes, flows are at a healthy level in both instances, but the question we need to ask ourselves is, “which direction are flows trending?” In May, flows tend to rise due to runoff and while rising flows are a good thing this time of year, dramatic increases in flow lead to off-color water, poor visibility and difficult fishing. If flows are sitting at 1,500 cfs because of a 600 cfs increase over the last two days, odds are, you’ll have a hard time locating and attracting trout. On the other hand, if flows are trending down, as they tend to do towards the end of July, 1,500 cfs will look much different than it did in May. As flows decrease, water clarity, visibility and fishing improve. Once you understand the importance of monitoring flow trends, the last step is understanding where the river sources its water.

Floating Lower Colorado River

In Colorado and many other western states, our rivers are typically freestones (rivers that flow freely without disruption from dams) or tailwaters (rivers that receive water from bottom feeding dams). To make things a little more complicated, there are some freestones that have a degree of dam intervention and/or receive water from tailwater tributaries, such as the Colorado River. There are also tailwaters that intersect with small freestone tributaries, such as the Deckers stretch of the South Platte. Understanding where the river sources its water is particularly important during the spring because it gives us a better understanding of the impact increased flows will have on water clarity.

The Middle Colorado River is another perfect example for this scenario. In April, flows increased by roughly 500 cfs. A material increase like this would lead you to expect that water clarity and visibility would suffer. However, the impact to clarity and visibility was minimal. The reason being, the tailwater section of the Blue River below Green Mountain Reservoir increased. Since tailwaters receive “clean” water from the bottom of a reservoir, the Colorado River was fed clean water rather than dirty water from one of its many freestone tributaries. Had the increased flows originated from runoff on one or more freestone tributaries, we would expect the water on the Middle Colorado to be dirty and off-color. Regardless of the situation, we need to be prepared to make adjustments and planning for those adjustments can make all the difference.

Here are a few tips to be successful during increasing and decreasing flows:

Increasing Flows

  • Large, messy and flashy/bright patterns are king
  • Get your flies into the deepest water column
  • Focus on the banks and other soft sections where trout receive protection from debris and faster currents
  • Size up your leader and tippet

Decreasing Flows

  • Pay close attention to hatch schedules or seine the river to understand what’s on the trout menu
  • Imitative patterns will help fool selective trout
  • Cover a lot of water and don’t rule out any section that is at least 2 feet deep
  • Size down your leader and tippet

For more details on runoff tips, tricks and fly recommendations, check out our other run-off focused blogs:

Spring Fly Fishing: How to Anticipate Runoff and Make Necessary Adjustments

Tips for Fishing Run-Off