How to Find Fish (Part 3): Riffles

This is the third post in our series on how to find fish in any type of water. To see all the posts in this series, click here. 

By Spencer Durrant

My wife and I used to live in a suburb of Salt Lake City. On the drive home from work or fishing, I’d head down a four-lane thoroughfare stacked with fast-food restaurants. With all the traffic during evening rush hour – and a grumbling stomach – I usually pulled into the first place with a short drive-through line to grab dinner. I didn’t much care where it was, so long as I didn’t have to wait too long.

That experience – crammed into traffic, surrounded by other hungry motorists, all of whom seemingly don’t know how to drive – is fairly similar to what trout experience when feeding in a riffle. The river moves quicker, and trout are more willing to compromise on a good drift if it means they have a chance at a large meal – kind of like the time I pulled into a Subway, even though I swore off their food years ago.

A riffle is moving quicker than other typical holding water, but fish hang out there because the opportunity for food is so high. The extra energy of swimming against the current is worth it if they get a steady stream of caddis tacos. Because riffles flow quicker than traditional holding water, I know many anglers who skip them entirely. These anglers are skipping some of the best opportunities to catch fish, especially if there’s a hatch on.

I don’t want you to miss out on the chance at some great fishing! In the rest of this post, we’ll cover everything you need to know about locating fish in riffles, and the best ways to present flies in this specific water type.

What is a riffle?

First off, we need to define what a riffle is.

Riffles occur when water flows over a high-gradient streambed that’s littered with smaller rocks and gravel. As the water flows over this steeper section of streambed, it hits the rocks and gravel. The water is forced to either side of the rocks, and sometimes even back upstream, if the water hits the front of a rock with enough force. All this extra movement creates the telltale signs of a riffle that us anglers are familiar with.

Here are a few examples:

Riffles can be short or long. The Madison River in Montana (last picture) is often referred to as “a long riffle” because the entire river is seemingly that same water type.

Often, you’ll find riffles occur between pools or deeper runs.

Why do fish hold in riffles?

I need to give a tip of the hat to Devin Olsen for his excellent work on riffles in his book Tactical Fly Fishing. Much of what I’ll share here can be found in fantastic detail in that book.

Basically, riffles create the perfect environment for aquatic insects. The rocks and other detritus littering the riverbed that create a riffle create a good buffer from the main current where aquatic insects can hang out. Bugs like to live in the small gaps between rocks, of which there are tons in a riffle. These small gaps combine with the buffer from the current the rocks provide to form ideal aquatic insect habitat. On top of that, the fact that riffles are shallower than other spots in a river means they get more of an impact from sunlight. That means more aquatic vegetations grows, which is the food source for aquatic insects. All of these factors combine to make a riffle the ideal habitat for bugs – and bugs are the main food source of many trout.

This is why you’ll sometimes hear riffles referred to as “the food factory” of a river – much like the four-lane thoroughfare example I gave earlier. It’s easy to understand why trout spend so much time in riffles, when you realize just how much food is available.

Trout also hold and feed in riffles thanks to the nature of riffles themselves. As water hits and moves around rocks – thereby creating the riffle – the water slows down just enough in spots that fish don’t have to expend a ton of energy to hold there. Even though there’s not an obvious seam on the surface of the water, the current is slower enough near the river bed for fish to hold comfortably.

Since riffles are moving quickly, they tend to have higher concentrations of dissolved oxygen. As water temps rise during the summer months, the amount of dissolved oxygen in slower-moving water decreases. Fish will automatically seek out riffles during the warmer part of the year not just for the food, but for the increased amounts of dissolved oxygen, as well. During the winter, that trend reverses. With colder temps and less sunlight, aquatic insects aren’t as abundant in riffles, so fish aren’t getting as big a return on their expenditure of energy to stay there. Fish will usually leave riffles to hang out in pools during the coldest parts of the year.

Finally, it’s worth noting that fish hold in riffles because the choppy service offers some protection from overhead predators. If you’ve ever tried to spot fish holding in a riffle ,you know how hard it can be to find them amidst all the bouncing water. Trout like feeling safe and protected, and riffles offer that.

Where do fish hold in riffles?

Generally speaking, fish will hold just about anywhere in a riffle. That’s why, if you look for any information about where to find fish in riffles, you’ll usually come away with a bunch of tips on how to fish a riffle. With riffles, it’s usually a good idea to thoroughly fish them, because it’s hard to predict exactly where the fish will be holding. It’s not like pocket water, where you know trout will hold in the seams.

That being said, you still need to give the riffle a thorough inspection before you start blindly casting. For example, you might find a submerged log, or a rock, behind which – as we know from the article on pocket water – there will be a cushion of softer water. These are excellent spots to cast to first, as it’s highly likely trout are holding there. Since riffles cause so much surface disturbance, an obstruction might not make the same surface waves we’re used to seeing, especially if they’re small. But as we know, trout will seek out any bit of calmer, slower water to hold in while waiting for food to drift by. If you see anything that looks like is might offer trout some shelter from the current in the riffle, cast there! You’re probably right.

How to fish a riffle

Now that you know fish are likely dispersed throughout a riffle – unless you see some obvious obstruction they might be hanging out around – it’s time to talk about how to fish this type of water.

You should have a couple of goals when fishing a riffle:

• Cover all the water
• Cover all the depths

Fish might be right on the bottom, munching on worms, scuds, and mayfly nymphs. Or perhaps they’re suspended in the middle of the column, eating both nymphs and emergers. Or, if you’re lucky, they’re looking up and willing to eat just about any dry fly with a decent drift. The fact that fish can be just about anywhere underscores the importance of covering as much water as possible.

Just like that old saying, about eating an elephant one bite at a time – don’t try to fish the whole riffle all at once. Follow these simple tips to help make it easier:

• Break it into sections: Focus on the head, middle, and tail of the riffle. Cover all the water in the tail, then move onto the middle, then the head. This approach works whether you’re fishing facing upstream, or if you’re standing to either side of the riffle.
• Adjust your depth: I like to fish riffles with a dry-dropper rig. Fish are more forgiving of bad drifts in a riffle, and they’re more likely to eat dry flies, too. I typically have a big dry fly, followed by two nymphs. I space my nymphs out so one is riding close to the bottom, and the other is somewhere in the middle of the water column. If you just fish a single dropper, play around with the depth until you start hooking into fish. If you’re fishing with two nymphs under an indicator, adjusting your depth is as simple as moving your indicator.
• Be thorough: Yes, fish feeding in riffles are forgiving of less-than-perfect drifts, but that doesn’t mean you’ll hook into one on every cast. Give every spot at least a half-dozen drifts to make sure all the trout have had a chance to look at your fly.
• Stay tight: Don’t let a ton of slack line come between you and your flies. Takes in riffles can be very subtle, and you’ll miss them if you have a ton of slack in your drift. Keep the drifts tight and close enough that you can easily set the hook on the smallest indication that a fish has eaten your fly.

Riffles in action

Back when I lived in Utah, I frequently fished a little stream that was well off the beaten path. I loved a particular section that was only accessible via a long walk on a steep dirt road. The road ended right where the stream flowed from tight pocket water into a large, broad riffle.

Within that riffle I could routinely catch 5-10 fish, depending on the day. The fish held in different spots each time, but they were consistently there, willing to eat my flies.

The tragedy is that I skipped over these riffles for years, focusing instead on the pools. Once I started fishing riffles more frequently, though, I wondered how I’d ever let such a great piece of water literally pass me by.

Chances are, your local fishery has a few riffles that go unfished. Pay them a bit of attention next time. Thoroughly cover the water, and who knows what you might catch.