River Algebra (or, Making Math Fun)


Minnesota angler Adam Olson hoists a bronzeback with great colors.

It’s that smorgasbord time of year when just about all finned creature are amenable to the rod and reel.  From brook trout to muskies, carp to cutthroats, the watery world is your oyster—and it’s yours from top to bottom.  So you’ve got to make some decisions, especially if you’re a warmwater river angler, as I tend to be during this season.  One of those questions we face is this: do I fish on top or somewhere down below?

Of course, you could let whimsy be your guide and do whatever the heck you feel like doing that day.  It’s summer, fish are eating, and you’ll catch a few (unless they’re muskies, of course, in which case all bets are off).  But if you want sound science and good logic to inform your decision, and you want more and bigger fish in the boat, then you need to look at the water you’re fishing and identify its primary structural features.  Is your river wide and relatively straight with clearly defined primary and secondary shelves?  Or is it small and windy, pocked with boulder and gouged with holes?  Making that determination will help you choose between two fundamental options: to throw poppers, wigglies, chuggers or sliders on a floating line or baitfish and crayfish imitations on an intermediate line.

Let’s imagine the river as having two axes: x and y.  The x axis parallels the bank, the current, and river shelves—those first and second drop-offs.  If fish are hanging on X axis structures, choose a floating fly.  Work it slow, wait a long time before moving it, and you’ll be covering a lot of that x axis structure.  This works best on rivers—and stretches of rivers—that are wide and gently meandering, as opposed to narrow and tortuous.

Those narrow, torturous rivers tend not to have stable, elongated shelf lines.  And in addition to their particular structure, there’s generally more cover to fish–sweepers and log jams, behind which form holes.  Let’s think of the line stretching from the bank to the boat as the Y axis.  Are there boulder and pockets and logs stretching out from you to the boat?  Great!  Try a baitfish or crayfish pattern and work your fly through these areas.  Vary the speed of your retrieve and make mends where necessary to keep the fly hitting the primest y-axis spots.

Of course, most rivers are going to possess a mix of these two types of dominant structure, so have two rods ready.  Or carry a diver.

A diver—be it a classic Dahlberg Diver or the new heir to the diver throne, Mike Schultz’s Swingin’ D, featured in an earlier article—let’s you fish both axes with relative efficiency.  Fishing these flies on a very slow sinktip, or on a floating line with just a few feet of T-11 or T-14, allows that fly to hang or even float back to the surface between strips (x axis territory) or dig down and dirty (that y axis again).

Thinking of the river as a grid may seem complex at first, but I’ve been around enough freakishly good anglers to know that it factors a lot into their thinking, even if intuitively.  When you’ve got 10 miles of river to cover, especially if that water’s new, looking downstream an anticipating structural features in advance can help you make the right presentation to the right water.