Here are some tried and true methods to read a river and increases your fishing success.
From the Yellowstone River to the Cumberland River to the incredible Allegheny River, there are fishing opportunities across the nation to be had in every state of the union. Although there are plenty of individual differences, most rivers can be fished with a few similar approaches, especially when it comes to reading the water.
Just as in real estate, location is the key in fishing. Anglers across the country know this to be true. Moving water can mean deeper water. What you see on the surface can be deceiving, which means slow water and even shallow water can be better or worse at holding fish depending on the conditions. Knowing how to cut out areas that are dead water is a big part of the answer.
Whether you are trout fishing or targeting catfish, fly fishing or baitcasting, most species will react in accordance with their environment when it comes to current, and live their lives the way their species has for generations. Fish holding areas may change over time in rivers since high water years can change the underwater landscape, but for the most part they will simply move to similar spots that have been created, just in a new location.
Reading a river and applying it to your fishing strategies takes time and experience, but some of the general commonalities and terminology from water body to water body can help wrap you head around it.
Fishing Fast Water
Thinking that fish don't live in the faster sections of a river is a recipe for failure, but understanding when and why they stay there is of the utmost importance. During the early part of spring when many rivers are under the influence of the winter melt runoff, fish can find themselves almost anywhere, just trying to survive the current.
Finding fish in faster water after a river system has moved through the season, settled down, and become its normal self is more about understanding what lies below, and that means depth and structure. For fish to want to lie in the current, there has to be a reason for it. That reason is the conveyor belt of food.
Outside bends in a river are great for this.
Certainly, fish will ride out the current breaks around the edges of the moving water to limit energy use, but some species like trout make a living in these areas due to their excellent eyesight and speed. For those who live to target Atlantic salmon, for instance, drifting streamers through the current can sometimes end only one way: hanging on for dear life while watching a bruiser launch into the air again and again trying to shake it.
Sometimes when observing a river or other water flow, the structure that can be seen can give you an idea of what can't be seen. For instance, moving water almost always has some kinds of rock formations for the many eons that the water flow has changed its course. These rocky outcroppings can allow an angler to see the differences in depths as the water flows around the boulders and better choose the best areas to cast.
A rock sticking far out of the water is more likely to have less depth around it than one that can only be recognized under the water by the swirl it creates in the flow. This is not always true, but it is a starting point. Either spot can be good based on the fact that the flow is interrupted and the water behind the rock makes for a good ambush point.
In areas where an angler is fairly certain of the depth as a fish holding area, those fish will usually be found at or near the bottom to give them a break from the faster flow. One of the first good ideas is to use fluorocarbon line since it sinks faster than braid or mono. Depending on if you're using bait or lures you will need to decide how much weight will give you a bottom-bounce feeling every two seconds or so.
This way you know that your offering is in the strike zone, but will not get snagged as much.
Jigs, sinking stickbaits, and inline spinners fished slowly can bounce the bottom for bass and aggressive trout in many rivers. Some opt for a Carolina rig tipped with a minnow, crawfish, or soft plastic to garner strikes in deeper water. If you're fly fishing, European nymphing may be a good bet, or anything that can get a fly down deep.
Fishing Slow Water
These areas are fairly obvious on river bends, behind rocks and boulders, and where merging currents come together. It's not that unreasonable to find slow moving water in centralized locations in a river or large stream where long, straight stretches of water have dug channels for many years.
Downed trees are great spots for locating slow water that can be adjacent to the faster flow on a river. These areas give fish a great resting and ambush point at the same location and an angler will often find multiple fish there. Fish use these areas for feeding, spawning, and as a loafing area. They spend time opportunity feeding, so whether they're truly "hungry" or not, they will often strike when your bait catches their eye.
Opposite of the outside bend in a river is usually a slower, more defined area of water that has spent many years cutting into the bottom since the flow digs a channel there, especially on a sharp corner. Known as an eddy, these are spots worth focusing on. This can cause a back-current or whirlpool effect, and serve as another place where fish will lie to rest and ambush prey.
On longer slow stretches it can be a bit more difficult to spot areas that fish are using. All of the water looks the same, so how can you decipher what's happening beneath the surface? Sometimes an eddy in the current can be seen indicating that there may be a large rock or sunken tree under the water, and anytime there is structure it can hold fish.
Where two separate flows of water on the same river come together it creates an area of merging water and provides a break in the current where fish congregate to take advantage of the food supply. These are areas where fish, which normally always face into the current, can travel and hunt in multiple directions without giving up their good vantage point.
Riffles are areas of the water flow that sometimes resemble small pointed waves, but are obviously moving. Here is an important tip: Look before you step into the riffle of a river, because fish can be right in front of you. Anglers that have fished locations like the fabled Yellowstone River know that a riffle is wadable, productive place to cast.
It's thought that moving water like riffles may contain more dissolved oxygen, giving fish two reasons to be there: food and comfort. An old fly fishing axiom is that the warmer the water, the more fish are using the riffles.
When temperatures warm up and water levels come back down further into the season, fish can certainly be found in these areas, but not all riffles are the same. Generally, you are looking for spots that are knee-deep and shallower, but focus too shallow and you are wasting time. Your offering should also be bottom bouncing to look as natural as possible whether you are fly fishing or floating live bait. It's a significant effort to begin to truly read and understand a complex riffle in a river, so be patient.
But also be nimble to a reasonable point. If you see fish in a riffle, you can assume they are usually there to eat, and if you get a couple clear drifts in front of them without a strike (and it doesn't spook), switch up your lure or bait.
Water clarity is a big factor in these areas. Fish can and will see you if you're not paying attention and will usually be gone for good. This is why it is almost always imperative to approach from the downstream side since the fish almost exclusively face into the current. This is not as much an issue in stained or turbid waters.
Rivers are used by kayak fishermen, boat fishermen, and wading fishermen from Montana to the Georgia, and they're all seeking ways to catch fish. Angling for big fish in these waters can be done in deep pools, faster current, and even open water for catfish, steelhead, or even smallmouth bass, but the fishing tips vary from area to area.
Sometimes reading a river is not so much unlike reading another body of water, and sometimes it is completely different. Signs of drop offs, bait fish, or even undercut banks can be very accurate in identifying fishing spots whether it is in slower water or deep water.
Rivers are born in their headwaters and usually ends at its mouth, where the water empties into a larger body of water such as a lake or the ocean. Rivers can also form estuaries, where saltwater mixes with freshwater near the river mouth to form brackish water, and both areas can be great fishing.
Rivers can be used for irrigation, drinking water, transportation, and to produce electricity, but their best use is for fishing, and we won't argue with that.