Riffles are among the most productive types of water in trout rivers and streams.
When we think back on so many of the places we've trout fished across North America, the places that are the most consistent for finding feeding fish are riffles.
The upper Madison River is a world-famous trout fishery sometimes referred to as "the 50-mile riffle". Very few rivers have so much productive water throughout their entire length.
A riffle is a relatively shallow stretch of water with current flowing across cobble rocks. These rocks will range from about the size of a baseball to a bowling ball. The swift, shallow water running over them creates a characteristic chop on the water. The swift current prevents any silt from depositing on the bottom of these areas. The rocky, uneven bottom provides vast surface area for aquatic insects to thrive since there are countless micro eddies with little no current between the rocks. These same discreet patches of dead water on the bottom also provide numerous locations for trout to lie comfortably in what appears to be uniformly swift water. Riffles are usually at the head of a pool or run of water and maybe quite shallow where they start. A riffle will become deeper as it transitions into a pool or long run of water that maintains current but is deeper than a riffle. This is important to consider when you are choosing whether not to fish a riffle or the deeper pool downstream. Riffles offer a combination of exceptional habitat for both aquatic insects and trout.
Stonefly nymphs like this, as well as mayfly nymphs and caddis larva, are commonly found in riffles.
Because riffles are hot spots for insect activity, they can also become a hotspot for feeding fish.
Decades of guiding anglers have shown us that while many anglers are aware of how good riffles can be, even more, have yet to discover this. As mayfly nymphs and caddis pupae ascend from the stream bottom to emerge, they are easy for a trout to pick off, and this is what makes riffles so good. Even seasoned anglers may not be aware of just how shallow some fish will get when the emergence of insects is at its peak. Large trout may creep up into the water only a few inches deep when food is abundant. Anglers should also consider that the choppy water in a riffle conceals their presence from predators as well as providing ample nutrition. Also, the distance from the bottom to the surface is minimal. That allows a fish to pick off both nymphs and adult insects on the surface without the need to move up and down very far.
There are a few catches when it comes to fishing riffles in spite of all the benefits.
If there aren't any insects hatching in a riffle, don't expect many fish to be there. Chances are good they will spend their downtime in the deeper water just downstream and move upstream as food becomes abundant. The extra energy required of a trout to hold in swift water will not be worth the effort if food isn't adrift. As fish begin to notice more and more food coming into the deeper water some will migrate up into the riffles to get the first shot at the food.
One important yet overlooked part of fishing riffles is casting accuracy.
While trout found in riffles are feeding with a high likelihood of taking your fly, they must see it. When trout are feeding in riffles, they don't get much of a chance to look at the food they eat. The swift current has it moving to them and past them very quickly. This is an excellent advantage for the angler, but at the same time, it also requires an angler to get the fly where a fish will see it. Since the insects are coming at the fish so quickly, they tend to develop tunnel vision. A trout will position itself so food should come right to it and focus on that narrow zone to the exclusion of everything else.
Smoky Mountain brook trout make use of small calm spots between rocks in a riffle to get the best shot at drifting food before other fish downstream
I've seen anglers put flies all around an aggressively rising fish that never made a move to their fly. What was the problem? Even though the fly was about one foot from the fish, it didn't see it. Eventually, when the fly came right to the fish, it ate without any hesitation. This looks easy if you put the fly in the right place on the first cast. It becomes maddening when your fly is all around a feeding fish but ignored.