Alluvial pools usually form along the outer bank of river bends through the process of erosion. Just like race cars that hug the high outer wall around turns to find the fastest path, the fastest current courses along the outer bank around river bends, which erodes a deeper channel along the bottom and against the far bank. Over time, the outer bank widens, eventually forming a deep pool, which initially traps slack water and foam. The process of erosion takes considerable time and pools show various levels of “maturity” depending on how far along it is in its development. As the pool matures, it encompasses reverse currents and even slow-turning whirlpools. Meanwhile, through the same erosive process, a gravel bar gradually forms along the inner bank in the last third of the river bend.
Alluvial pools lack the consistent structure of high mountain pools, making them a bit more challenging to fish. But take a moment before you begin to pick out the transitional areas and identify a trout’s best feeding lies. Then choose the best fisAlluvial pools lack the consistent structure of high mountain pools, making them a bit more challenging to fish. But take a moment before you begin to pick out the transitional areas and identify a trout’s best feeding lies. Then choose the best fishing method for each area and the best positions to do it from.
hing method for each area and the best positions to do it from. The features of alluvial pools are not as consistent as highaltitude, hard-bottomed streams, and vary most based on the maturity of the pool. In mature pools, the whirlpool along the outer bank and the gravel bar along the inner bank compress the feeding lane into a narrow corridor, creating excellent feeding lies along either edge or the bottom. Immature pools have less dramatic transitional zones than those that are more mature, but in general, look for the best transition zones along the face and back edge of the gravel bar and also between the fast water and the slack or reversing water along the outer bank.
To fish alluvial pools, you can reach the main feeding lane and transition zones from a wading position on the shallow gravel or sand bar along the inner bank, or by reaching over the back eddy part of the pool from a position standing on the outer bank. From your position on the gravel bar, tight line nymphing should work well, casting upstream into the fast flow. Standing on the outer bank, tight line techniques may or may not work, depending on how far you have to reach to get over the eddy. Because of the distance to the feeding lane, you may need a floating indicator to effectively nymph fish it. Even with an indicator, you’ll probably need to keep the fly line from contacting the slack or reversing water of the main pool.
The backwash of the pool collects foam and other floating debris, including insects after emergences and spinner falls. With an upstream or downstream presentation, drift a dry fly through the fast flow and let it eddy out into the pool—into the slack or reversing flow. You might just find a trout still feeding long after an insect event— possibly a fish sipping on spent spinners or crippled emergers.
From the outer bank at the head of the pool, you can also dead drift a Woolly Bugger or streamer down the lane of fast flowing water and then twitch it through the seam into the slow moving water of the pool. This imitates a fish caught and carried in the current that’s swimming into the slack water. Wet flies or even soft hackles fished in the same manner can be equally effective. Don’t forget to try your Woolly Bugger or streamer along the backside of the gravel bar before you call it quits. The back edge of bars serve as staging areas for subordinate trout; those too low in the pecking order to command good feeding lies are forced to wait in staging areas until one opens up. Large trout frequently maraud these edges looking for an easy meal.
No matter which type of pools you fish in the course of your day, a moment’s consideration will tell you not only where to fish, but also how to fish each of them. While I admire Bergman, I don’t have the discipline to spend an afternoon studying a pool from the shore. After only a few minutes, I fall prey to the siren song of the pool and the trout that lurk in its waters. In other words, I’m like any other angler—I pick up the rod and fish.
Jason Randall is a frequent contributor to American Angler and the author of the Fly Fisher’s Guide trilogy. His fourth book, Nymph Masters; Fly Fishing Secrets from Expert Anglers was released from Stackpole/Headwaters Books in April 2017.