Understanding river conditions and what causes these variations will allow you to forecast the quality of the water long before you plan a fly fishing trip.

Understanding river conditions is an important part of fly fishing. Rivers, especially western rivers, are controlled by several natural causes including snow pack and temperature. And, for the most part, you can forecast year to year about when they’ll reach flood stage and recede back to a wadeable level.

Understanding River Conditions

Having a basic knowledge of how a river changes throughout the year will help you forecast the water long before you plan a fishing trip. For example, where you’ll experience great winter fishing in the middle of March, you’re liable to find the same river at flood stage (think rapids) just a few weeks later in April. You may hear the following terms to describe river conditions whether you’re on the United States Geological Survey (USGS) website, standing in a fly shop, or talking to us about when to book a day fishing.

River Stage

River stage is essentially the height and flow of the river. The way the USGS measures river stage is by some arbitrary point where the river bed equals zero. An ideal day for fishing would be around what’s called baseflow conditions – a couple feet deep. That same river could quickly rise 15 feet in a matter of hours if a big rainstorm hits. Or a more gradual increase as temperatures warm and snow melts. Gauging annual river stage becomes second nature to resident Colorado fly fisherman though maybe not so much to out of staters. If you aren’t sure, ask us and we’ll give you a report. 

Snowpack

Snowpack, or the amount of snow that falls in the mountains and doesn’t melt for long periods of time due to freezing temperatures, is important to a river’s ecosystem. It’s also important to fishermen who must understand how snowpack affects river conditions throughout the spring and into the summer. 

Water runs downhill. And the amount of snow the mountain receives throughout the winter will inevitably cause river conditions to change once temperatures warm and it begins to melt. It’s a trickle effect, if you will, where melting snow turns to water which runs downhill and accumulates in creeks which dump into rivers. 

April and May are usually the months most affected by snowpack. On big snow years it’s possible for rivers to run at flood stage well into June. While rafters and kayakers might enjoy this, it’s not good for fly fishing in the moment. 

It is good, on the other hand, for fly fishermen from a conservation standpoint. With scant snowpack comes shallow rivers that recede to dangerously low levels in late summer. Water temperatures rise and the smallest amount of stress, as in getting caught and released, can kill trout. In many areas in the west, it’s winter snows, not spring or summer rains, that sustain a river throughout the year.

Turbidity 

Turbidity is the clarity of the water. Think of the water that comes out of your kitchen faucet. It’s clear, which means low turbidity and for the most part, which equals high quality. The ditch out by the road from your house is probably streaming muddy water after a big rain. That water is highly turbid and likely not so safe to drink.

Scientists measure turbidity by measuring the amount of light that is scattered by material in the water when a light is shined through the water. These materials include clay, silt, algae, plankton, and other microscopic organisms just to name a few. For a fisherman, turbidity can usually be determined pretty quickly as you’re looking into a river when the sun is shining.

As snowpack melts, it increases river stage and turbidity. Trout hunker down when the current is running rampant and won’t eat what they can’t see when the water is murky. But if you can catch them either right before or right after runoff, you’ll experience a feeding frenzy rarely seen throughout the year.