Guest Blogger: Joe Dellaria, Woodbury MN

Three days and three completely different patterns for where the fish were and which fly the trout preferred. This is what trout fishing is all about. A big part of being successful at stream trout fishing is problem solving. Every day is a new day with its own unique weather and water conditions. Sometimes you can get a couple of outings in a row where everything is the same but that is rare.

Patterns begin to emerge the more you fish. Keeping a fishing log can help put those patterns together. Recording the date, a brief description of the weather, water clarity, time of day, where fish were caught and what they were caught on will help piece the patterns together.

There are a couple of simple maxims to keep in mind as you start fishing on each outing. First, fish tend to hold near areas where current brings food past them. They rarely hold in fast current unless there is an obstruction or a depression in the riverbed breaking the current. Holding in fast current requires extra energy. Unless food is plentiful, a fish cannot afford to expend more energy in the current than it will gain from the food it can eat.

Second, the fish is both predator and prey. Fish avoid becoming a meal by hiding while they are eating. They will use obstructions, riffles on the water surface, overhead cover, and water depth to hide while they are feeding. Your job is to identify areas where slower water is near faster current to provide a holding position while the fish waits for food to drift by.

Most rivers have more areas meeting the two criteria above than you can possibly cover. How does one consistently figure out which spots are going to be best the day you are fishing? Two key elements are the water level and water visibility. The water level is easy to understand. If it just rained for two days straight, the water level is going to rise several inches to a couple of feet. This means that areas providing slow current to hold in next to faster current will be in different places than before it rained. Hence, you need to fish in different areas depending on the water level.

When the river is high, it is generally a good idea to focus on obstructions near the river’s shore. Conversely, if it is in the middle of a drought during the summer, the optimal holding areas are going to be near obstructions in deeper water. Water level is straightforward to understand.

Water visibility is a bit more complex. I like to think of it in terms of how deep the water is where I can see rocks, pebbles, or debris on the bottom clearly. There are two primary factors influencing how deep you can see into the water. First, there is the available light. Is it day or night, clear or cloudy, midday, sun up or sun down? The brighter it is the deeper you can see. Secondly, the water clarity must be considered. Is the water clear as gin, stained, or full of particulates from run-off? All these factors influence the overall water visibility.

The interplay between water clarity and available light produces the water visibility. The chart above provides shading to show which combinations produce high, medium, and low water visibility. To illustrate the point, the water visibility for a few combinations are given below:The following are rough guidelines for water visibility conditions. These are provided for the sake of the following discussion:

* The provided depths are a guideline and may be different on other rivers. The point is that water visibility changes where fish are eating.

It may seem that water visibility is like following water clarity. However, the two are significantly different when it is dark. Water clarity is not useful when it is dark. When it is dark, you cannot see the bottom (unless there is a bright moon). Assessing water clarity alone would lead one to believe the water visibility is high. Since water visibility is the combination of water clarity and available light it correctly assesses the water visibility as low (In Parts 3 and 5 I will discuss how the water visibility influences where the fish hold to eat..).

In the same way, it is not useful to use available light alone to assess the water conditions when the water clarity is low. Using available light alone on a bright sunny day where the water clarity is low, would suggest fishing in deeper areas. Since water visibility uses both water clarity and available light, the conditions would be either medium or low water visibility; that would suggest fishing cover in shallower water. How shallow would depend on whether it was medium or low water visibility.

This part of the article was intended to provide a primer on what water visibility is and how other factors influence fishing success. Part 3 will use the definitions of low, medium, and high water visibility to see how the water visibility played a role in where fish were caught on the three different days in Part 1.


  1. A good parsing of the predominant factors for this discussion Joe; I look forward to reading the remaining parts.

    As a long-ago post played with, I believe fish probably don’t assess how visible they are in choosing their feeding stations; I suspect their general aversion to light is what saves them from holding in stupid places. As you point out, available light is part of the picture, but if some other factor is attenuating that light (water cloudiness, foam on the water, riffles that chop up and disperse the light, a big overhanging tree, a log, whatever), then they feel more free to hold in, and hunt in, such water. Just a theory, mind you, as it’s possible they’re geniuses and have carefully measured how visible they are and have reasoned it all out (but I’m not buying that because if they were geniuses they wouldn’t be hitting most of the pitiful flies I tie).

    One point you made, “Unless food is plentiful, a fish cannot afford to expend more energy in the current than it will gain from the food it can eat” always stymies me, because I often see large trout heaving themselves bodily a foot above the surface for the purpose of going after some flying bug that’s no bigger than the point of a pin. Why, on earth??? I guess some bugs taste better than others.

    Looking forward to the rest of your article!

    – Mike

  2. Hi Mike,
    I think you summarized it well in the first paragraph. When the water is clear, fish intuitively feel vulnerable and move to places where they feel less vulnerable. Those that don’t, generally are removed from the gene pool when they become food for some predator.
    As for large trout heaving themselves out of the water, I have seen some decent sized fish do that too. In most cases, I can’t see anything they are after in the air. I have no proof, but based on the lack of nearby prey, I think they are doing it for fun. Or, as you suggest, perhaps they are geniuses and are taunting us for our pitiful attempts to catch them. If so, that’s a 15 yard penalty with a loss of down!
    Let me know what you think after you see the rest of the article. I try to tie things together.
    Tight Lines, Joe

    1. I look forward to the last two installments Joe. Right now I’m picturing a “spectrum” diagram of some sort, to help me keep the basic tenets in mind. It’s a great topic and a better one to keep in mind even than fly depth–because it helps identify what that productive depth is likely to be. Can’t wait to read the rest.

      Regarding trout jumping for tiny bugs or even just for fun, I think we’ve all heard the reigning theory for why they jump right in front of us for no apparent reason: It’s because they don’t have middle fingers.

      – Mike

  3. Hi Mike,
    You nailed it! Just yesterday a nice fish jumped just upstream of me. I thought it looked like he was waving his pectoral fin, but it was likely his best attempt at showing me his “middle finger!”
    Tight Lines, Joe

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