Guest Blogger: Mike Cline, Bozeman, Montana

photo1As hard as I might try, I really can’t find where they come from. They are always there, always (eventually) moving downstream. There always seems to be an endless supply of them—the bubbles–thin spheres of liquid enclosing air or another gas. It never seems they are alone either, showing great affinity for their kind. They will gather in small or large groups, cavorting and mustering in ways that make their presence even more obvious. Of course, they float along the surface of the stream and like the words on a page they provide great insights into the plot of the novel we call the river. I must admit I pay little attention to them in familiar waters, but on new water or in times of great variations in flow, bubbles are very important to the angler.

The study of the behavior of liquids is known as hydraulics and fluid mechanics. Within the field of hydraulics, we as anglers are concerned with Open-channel flow characteristics or the behavior of liquids in a channel with a free surface—Voilà—the rivers, streams and creeks we fish in every day. But luckily for us, we don’t need physics or engineering degrees to understand the important things we as anglers need to know about stream flow. In this case a picture is worth many words.

photo2Given that trout and other stream dwelling Piscis seek their place in the flow to either feed, rest or shelter, we know, at least in theory, where they might be and where they won’t be. The more experienced the angler, the more intuitive they probably are about what’s going on under the surface. Anglers are always searching for those invisible seams and areas of flow turbulence that provide respite from the current as well as conveyer belts of food to resting or feeding fish. Although the actual seam itself might be invisible, much like the Invisible Man, there can be clues to its presence. One of those clues are bubbles.

Bubbles are lazy things with little ability to do their own thing on the river. In essence they are at the mercy of the flow, the currents, the streambed and the ragged edges of the river. But such laziness provides great advantage to the angler who can read the bubbles and the insights they provide. One of my favorite fishing books is How to Find Fish and Make Them Strike, Joseph D. Bates Jr. (1974). The drawings and photos in the first three chapters of the book—The Basics of Finding Fish, Locating Hotspots in Rivers and Finding Fish in Streams and Brooks—have guided me for some four decades of fishing. There is one particular drawing that relates well to the ubiquitous bubble. A cross section of stream flow discloses that the water at the top, the bottom and edges of the flow is slower than the water in the middle of the flow. The water at the left and right is a bit faster than the water at the top. The complexity of the flow is compounded by invisible seams between water moving at different speed. These invisible seams or transitions in the stream are favorable to both feeding and resting trout. The deeper the water, the greater the difference between the speed of the middle flow and the surrounding edges. For the trout, deeper water not only provides better cover, but faster flows provide more opportunities at food caught in the drift. This is where the ubiquitous, but lazy bubble comes in.

photo3Once that bubble gets trapped in the flow, it will stay on the surface, but gravitate to faster water. It can’t escape it on its own. The bubble has no motive power other than its host, the flow or the wind. The only escape available from the flow is the surface turbulence caused by transitions within the stream flow due to obstructions in or on the edge of the stream. The classic streamside eddy is the best example. The eddy is caused by some obstruction upstream creating a seam between the faster flow and slack or swirling water along the river’s edge. Although eddys are not hard to spot, the behavior of the bubbles that get trapped in them can provide some real clues as to what might lie beneath.

photo4The little eddy in the photo to the left might not be there in higher flows, but on the Yellowstone at this flow level, a small eddy is formed. The cavorting and mustering bubbles create a foam roof that provides excellent cover for trout. The probability, that on the day, there would be fish holding along the seam that marked the right edge of the foam was high. There was, a 10-inch brown. On closer examination, the water depth under the foam was about 6 inches deeper than it was upstream and downstream. The foam roof not only gave away the eddy, but the eddy created a small patch of holding water with a nice cover on top.

On many rivers, bubbles cavort and muster to the point of creating large, marshmallow like piles of foam. These occur in places where bubbles are in the fastest flow, but encounter obstructions that extend below the surface. They can’t go downstream, so they pile up, sometimes over a foot high into big, marshmallow type foam pillows. Where ever you encounter this big pillows of foam, there is likely a deep, sheltered lie with a good current seam.

Placing your fly close to these foam pillows and allowing it to either swing under or close by can bring out some good fish.

photo5Apart from eddys and foam pillows, the bubble seam is your best clue in unfamiliar streams to good holding water. As you look across the stream, try and find the densest, but fastest flow line of bubbles. On big rivers, these might be anywhere. On smaller, meandering streams, bubble seams are generally found along deep outside bends or along deep straight channels. Those dense, but fast moving bubble seams bely what’s below, deeper, faster water with good transition seams.

Bubbles are not the end all, be all to reading good trout holding water, but they do provide clues. When you catch your next good trout in a nicely flowing river, stop and look at the bubbles and foam where the trout came from. You may never find out where the bubbles came from, but those cavorting bubbles when they muster are just another clue to make you a better angler.


  1. I remember being told by an excellent guide on a one of my trips out west that “foam is home” and it has always stuck with me. This is an excellent explanation of why that is. I’m hoping to find the book you referenced and learn even more- to help me get through a cold winter… thank you for the great information.

    1. David,

      Probably the easiest method of getting your hands on How to Find Fish and Make Them Strike is Lot of inexpensive copies there.

      May the foam be with you.

      Mike Cline
      Bozeman, Montana

      1. Mike-
        I found it on Amazon and it will be here tomorrow. Looking forward to
        reading it over the winter…
        Thanks again for a great article.

  2. I’ve used bubbles as indicators to help me identify covergence seams–lines of water between a laminar current and an eddy, or between currents of two different speeds that are converging together–so that I can identify slack water or “cushion” right in front of a rock or log. One does this when running whitewater too–in fact that’s the essence of reading water for purposes of navigating it. (It’s similar to identifying “cloud streets” that represent convection instability lines stretching out downwind of peaks.)

    And I’ve cursed foam because bubbles that remain more than a second or two tend to signal the presence of water impurities of one kind or another–sometimes natural but too often not. The surface tension is enhanced by surfactant and emulsifier agents and allow bubbles to linger, and then clump together as foam.

    But I’ve never thought of ceilings of foam that dam up in a corner of an eddy as hideouts for trout. Makes perfect sense–anything that cuts visibility is protection against prying predatory eyes.

    I’ll look at blobs of foam in a whole new light now; thanks for that tip Mike.

    – Mike

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