Identifying Prime Fall Fishing Structure

I received an email recently requesting further clarification on fall river structure terminology. As it turns out, this is a great topic for a quick post.

In the day to day rigmarole of balancing fly orders, updates, and the like I often lose sight of the fact that while many may enjoy the site content, some have no idea what I’m talking about.  That said, here’s a crash course on our site terminology.

Diamond Chop & Nervous Water:

Boiled down, this is the agitated water created by a transition in river structure. Basically, when stream depths change from shallow to deep and water speed decreases, it creates what we call diamond chop or nervous water. It’s not machine washy and turbulent like fast water rushing over shallow, exposed rocks, or like calm, flat water often found in deeper runs and pools. It’s the in between type of water.

Look for Pink Cahills to hatch out of these throughout the fall season. It's also a good piece of structure to plop a Hopper or skate an October Caddis.

What does diamond chop look like?

Current Seams

Often times, sub-structure and changes in water volume create varying currents and speeds within the river. The areas where these varying currents overlap create a ‘current seam’. This is an abrupt and noticeable change where fast water meets slow water. Seams are important because they condense aquatic insects in all parts of the river – as nymphs and larvae in the water column as well as emergers and adults on the surface.

Many times you'll find sublte rises on the inside 'slack water' edges. Fish like to hang in these areas and hoover Midge and BWO scraps.

What do current seams look like?

Soft Edges

Soft edges are fairly easy to identify – especially in moderate flows. They consist of the slower moving flat water along quiet inside banks. These are typically devoid of subsurface structure and crop up as rivers bend and current speed decreases.

Look for distinct 'head and tail' rises on the soft edges below heavy riffles. Often times you'll see fish stack up in these and pick off PMD, Pink Cahill and BWO duns as they dry their wings on the surface.

What do soft edges look like?

Troughs

These are long cut-outs in the main (center) gut of the river. If you need a visual, imagine dragging a melon baller along the length of cantaloupe half – a consistent depression in the river floor if you will. These are often found in moderate-depth (three to four feet), slow moving runs and can extend long distances down stream.

These are great areas to find Midges and BWOs early and late in the day.

What do troughs look like?

Rock Gardens

Rock gardens are great ‘onesy/twosy’ type areas. They provide relief from the current and are somewhat of a ‘catch-all’ in lower water. You’ll find fish holding between pockets feeding on knock-downs, duns and cripples that are blown into the bank.

You’ll want to approach these from the rear and scout for dimples before blind casting. Often times these are one shot opportunities so make your cast count!

What do rock gardens look like?

Side Channels

Plain and simple, side channels create obvious current seams. Look to fish these as they dump back out into the main current of the river. Often times, there will be a ‘gut’ (sweet spot) where the side channel cuts a depression into the main river floor. Look for fish holding in this water. The inside (slower moving) seams are great areas to find sipping heads and the outer edges are great for nymphing.

What does a side channel look like?

Flats

These are the areas that are a little tougher to gauge. They may not look like much, but when they turn on, they’re really on. Flats are typically void of structure, about knee to hip in depth, and are characteristically long – 100 to 200 yards in length. Fish will spread out within the flats so wade cautiously and target individual fish. These tend to fill up in the fall and spring and it’s easy to get distracted by multiple rise forms.

It's not uncommon to see 'mats' of PMDs and BWOs emerging from flats. Fish can be picky so watch the rise form -- some will be on emergers, some will be on duns, and some on cripples. Rarely do fish feed indiscriminately on the flats.

What do flats look like?

Obviously there’s a lot of structure to look at out there, and many of these will overlap, but this should get you started. Feel free to contact us if you have any other questions.

Here are a few tips to keep the bend in your rod:

• First, be mindful of the shadow you’re casting – not only from your body, but from your line. Keep false casts to a minimum and try to place flies as delicately as possible (drag free). If you’re not familiar with 'stack casting' then I’d suggest you get acquainted as quickly as possible.

• Second, long leaders and light tippets are an ABSOLUTE must. Lower flows create funky micro currents, so you’ll want a little wiggle room to eliminate drag and unnatural presentations. Likewise, slow, gin clear water allows fish a lot more time to examine your offering. If your fly doesn’t look every bit like a natural, you’ll likely get snubbed.

• Next, keep tabs on where fish are holding in the run and move into position accordingly. Make slow movements and take your time. You’ll also want to identify how the run is structured. Are fish holding in soft water off a current seam? Are they in the gut of the tailout? Holding in the flats? Tucked up in some slack water along a protected bank?

• Finally, you’ll want to pay attention to individual fish. Many times you’ll get out on a flat and see multiple fish rising throughout the run. Don’t assume all the fish you see are targeting the same type OR stage of insect. Some may be on duns, some on emergers, some on cripples…and so on. Pay attention to the rise form and do your best to identify what individual fish are eating. Pick your fish, know the rise form, match bug, and then make a smart cast.