In small to mid-size rivers, catfish tend to be small to mid-size, too. There are exceptions, of course, but if you’re after a trophy, this is not the type of water to focus on. Although channel cats are the primary species found in these rivers, flatheads and blues can also be present, especially in the lower ends. North America is covered by countless miles of rivers, most of which fall into this category. Not all of these contain catfish, however. Certain characteristics of a river determine whether it is suitable for cats. Among the most important of these are gradient and bottom composition. Gradient is the slope of the streambed, which determines current speed and bottom composition. Rivers with a high gradient have a fast current and a hard, rocky bottom; those with a low gradient are slow-moving and have a soft, silty bottom. Channel catfish are most abundant in rivers that fall in between these two extremes, those with a moderate flow, meandering stream course and rock-gravel bottom. Flatheads tend to do best in slower-moving streams with abundant woody cover. Although blues inhabit theses stream types, they seldom are found in any numbers. In areas where rock and gravel underlie a stream, these rivers form a series of rapids and pools. Understanding these structures and how catfish relate to them can improve your fishing. RAPIDS-POOL. Rapids  form over hard bottom and are shallower than other spots in the river because water can’t erode the bottom material. The gradient is higher here, and often the river is narrower, causing the water to move faster. You can see the rapids because the water boils up, and it is often so shallow there are exposed rocks. Below the rapids, the fast water carves the channel deeper. The water through this stretch is quite turbulent, often creating standing waves and whitecaps. This is where the pool forms, an area of slower moving water that may be several yards to a half mile long. At the head of most pools, there is a depression, or hole. The rapids’ churning water scours the bottom here, creating the deepest part of the pool. Below each hole, the river’s flow slows. Sediments fall, and the downstream end of the pool gets shallower, until the water encounters another area of hard bottom. Another rapids forms, and the sequence begins again. Rapids, pool. Rapids, pool. Holes within a pool are the best places to catch catfish. Cats travel through rapids when moving from one part of a river to another and sometimes make short forays to these areas to feed. They seldom stay very long, however. Holes, on the other hand, provide depth, current, food and security – everything catfish need to feel at home. The holes’ deepest portion is the den, or bedroom area, where cats can rest out of the current. The upper end is the kitchen, where cats feed. Rocks, logs and fallen trees in the deeper, upstream end of the hole make it even more attractive to catfish. Cats wait in ambush behind these current breaks, darting out to gobble up food, or bait, that passes by. Cover objects in portions of the hole where current is less or water is shallow aren’t as likely to hold catfish. When rivers of this size run through bottomlands where rock and gravel are limited, the rapids-pool structure is much harder to discern. It is present to some extent, and cats still favor the deepest holes. In this situation, a depth finder can be extremely beneficial for determining the best fishing spots. CURRENT SEAMS. These are created where fast and slow water merge.  Baitfish and other food items collect along the seams. Catfish gather in the slower portion of the seam to take advantage of these conditions. Current seams form downstream of bridge piers, big snags, logjams, shoreline points, large boulders and islands. Tributary junctions usually have two seams, one on the upstream edge and one on the downstream edge. Work baits along the slower edge of the seam for the best action. EDDIES. These form where current reverses direction due to water deflecting off a shoreline point or other obstruction  At the point where the current reverses, a mini-vortex – the eddy – develops. Like current seams, the slower water around the eddy provides an ideal ambush point for hungry catfish. BOULDERS. Large boulders may be difficult to find in deep water without electronics, but shallow ones should be visible to the naked eye. Most active cats are near bottom on the upstream edge of boulders, with a few positioning near the crown and boil-line areas. Cats in slack water behind boulders are usually inactive. LOW-HEAD DAMS. These were built on many small rivers back in the 1940s and 1950s as flood control structures. They are a barrier to fish migration, so in late winter and into spring catfish can be found in their greatest numbers below a low-head dam. A large scour hole forms just below the apron of the dam where the current flows over. This slack-water area is where the majority of the catfish hold. The best way to fish a low-head dam is to anchor well downstream of it and make a long cast up to the slack-water area below the turbulent water. Avoid a positioning too close to the dam; the powerful undertow can suck even a large boat under. CHANNELS TO BACKWATERS. On streams with adjacent backwater areas, the channel  connecting the two can be a great catfish magnet, especially when the channel has some current. Focus your efforts on backwater channels that are at least 4 feet deep, have cover such as stumps or rocks, and lead to a backwater that has deep enough water to draw feeding or spawning catfish. A good time to fish these channels is just after the spawn when hungry fish are moving out of the backwaters, or during a slow rise or fall of the main river. Backwaters and channels that remain deep nearly year-round are good ones to fish at night, because big fish that are on the move feeding frequent these areas. LOGJAMS. In slow, meandering streams, logjams or snags as they’re often called, are the primary habitat for catfish. This kind of cover can be as simple as a downed tree or log in the river, or as complex as multiple dead trees that have washed downstream and hung in an outside bend. As a rule, the best snags are large, consist of multiple trees and branches, and are found in water deeper than 3 feet. A logjam of this size can hold numbers of catfish, especially if it is located in deep water. Smaller snags such as a single tree or branch may hold only one or two fish. In rivers where logjams are the primary habitat, catfish can be found in them nearly year-round. To catch catfish in small to mid-size rivers, it’s also important to understand seasonal movements that occur. During some seasons, catfish may be almost totally absent from long stretches of water. It helps to understand why, and where they go. A study conducted in the lower Platte River in Nebraska, a tributary of the Missouri River, exemplifies the movement patterns existing in many such waters. Thirty-eight adult channel cats implanted with radio transmitters were released and tracked. Their movements showed distinct seasonal trends. According to the researchers, their movement patterns suggest downstream movement in the fall and winter to deep scour pools in the Missouri River, where the fish overwinter. In spring, there was a heavy movement upstream to spawning and feeding areas, where they spend the summer. These movements are most likely in response to changing temperature and/or discharge patterns in the river. The researchers also discovered that juvenile catfish prefer areas of intermediate depth, while adults favor the deepest water available. Both life stages tend to use areas having slow to moderate current velocities. Adult channel catfish have a strong preference for areas with log snags and rock revetments along the banks of the river. These structures create areas of deep, slow-velocity water where adult catfish can find a refuge underneath or behind an object. Studies in other areas suggest blue and flathead catfish also undergo seasonal migrations of this sort. And while we can’t say channel catfish always behave the same in other waters, the movements described above are similar to those observed in many other small to mid-size rivers. Applying knowledge of these movements can help anglers determine where catfish are most likely to be throughout the seasons, thus increasing the chance of catching fish. HOLES are one of the best locations to catch catfish in these types of rivers. The most productive ones are found on an outside bend of the river and have structure present on the upstream side, such as timber or large boulders. Holes are also found midstream just below a stretch of rapids, or just downstream of man-made structures such as dams and bridges.