Riffles are one of the most overlooked water type. They occur when the stream bed or rocks disrupt the current's flow in shallow water. They can be recognized by little surface waves/white caps (see picture below).
Why do fish hang out in riffles?
1. Food availability
Because the water is shallow, it receives more sunlight ☀️ . More sunlight leads to more plant growth 🌱 . With more plant growth comes a larger population of plant eating aquatic insects a.k.a. trout food. In addition, the faster choppier water can easily dislodge hiding insects causing them to drift in the current. If a trout is holding in riffles, it's there to eat!
As water temperatures rise ↑ , the amount of dissolved oxygen in the water decreases ↓ . Adequate oxygen levels are essential for both bug and fish survival. Thus, trout will generally be found in riffles more often during warmer months. Summary — fish will seek out higher oxygen levels (riffles!) as water temperatures increase.
The broken surface water creates security from airborne predators 🦅 . This can even include fisherman who pass by riffles because they don't, "see any fish."
Although the water is shallow and uninviting, it definitely holds fish. Do not overlook this water type the next time you go to the river!
What is the best way to fish riffles?
We'll answer this question with a real life example.
One winter one of our favorite streams here in Utah, we walked the banks looking for slow deep pools (where fish are usually found at lower water temperatures). On our way to the next pool, something caught our eye... within an area of riffles a fish's silhouette stood out. Then two.. three.. four.. an entire pod of big rainbow trout! All of them were grouped together in the fastest, shallowest part of the stream...
So you've found a pod of big rainbow trout in some fast moving riffles, where do you start?
First, we need to recognize that fish within riffles are eating food as it drifts by at a quick rate. Your flies need to be at or above eye level or they won't even be seen. Depth is key 🔑 . Start shallow and work your way down. Note the faster and shallower the riffles, the more likely fish will be to come up after a dry fly.
Second, controlling your line is very important. As soon as your flies hit the water, a fish can strike. As mentioned above, fish within riffles are used to food drifting by at a very fast pace. Independent of which type of rig you decide to go with (nymph, dry-dropper, etc.) use as little line as possible without getting too close and spooking the fish. Keeping tension on the line will help you detect and react to quick strikes.
Being winter, the fish had been keying in on small midges. We tied on two nymphs without an indicator (no indicator helps to keep the flies/leader/tippet in your control) and drifted them past the fish a few times. Nothing. We added a small split shot. As few more drifts... nothing. Another small split shot... BOOM 💥 , fish on! 🐟 Our decision to give riffles a chance paid off.
You've now added riffles to your arsenal of water types. Next we'll be discussing eddies.