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River Topography – An Angler’s Perspective
Just as every lake is different, so too are rivers with some of them offering conditions that are great for a particular species while others can be more generalised. It all depends on the source, how many tributaries flow into it and the type of terrain that they flow over. The result is a great diversity of rivers with some of them famous for species such as trout, like the Test, and others for barbel, like the Severn, while others will be good for dace or roach or pike or indeed any of the other species indigenous to Britain.

Every river follows more or less the same journey. Rain from mountainous or high terrain starts to flow downwards, its ultimate destination the lowest point which, in the case of our rivers, is the sea. Along the way it is fed by tributaries so that it becomes larger and more powerful. Speed and volume increase and so does the current, which impacts virtually everything else, carving out, over time, deeper and wider routes for its journey to the sea.

At the start of its journey, it may be very small and shallow, running quietly over stone beds where species such as brown trout thrive on the small insects carried along in its grip. It twists and turns, with every change of direction steering the current into a new path, with the result that the current scours out the bottom to form deeper channels more attractive to the fish. Take, for example, a left-hand bend leading into a fairly straight section of river. This concentrates the current to the right so that the depth is greater on that side and remains so for as long as that stretch of river runs straight. If the next bend is a right-hand bend then that position reverses, with the current gradually carving out deeper water on the left.

A visual clue to this is that often bankside vegetation, including trees, is often denser over the bank with the deepest water. That is ideal for fish, of course, providing them cover from aerial predators at the same time that occasional meals are provided by insects falling from the trees and other vegetation. It also gives the angler plenty of places to investigate. The two following diagrams illustrate the normal course of events when a river meets a bend in the way.
Sometimes the river will be swelled by another tributary, a second river flowing into it. Where the two meet is called a confluence and, while the current is generally made stronger, the exact effects will be created by a combination of the speed of the current, its direction and the volume of water being transported. In the next diagram, two roughly equal rivers flow into one from opposite directions, with the result that the current is broadly funnelled into the middle of the river. In actual practice, this is not so simple since the current might be much greater in one than the other and their paths very different, skewing the current rather than centralising it. In practice, you need to look and use common sense to judge the results. You will usually be able to see where it is running faster or deeper.

Every obstacle to the river will have an influence upon it. Some will be manmade, constricting or changing the flow, while others will be natural and may even be simple as a large boulder. The current will be deflected by this, giving predators the chance to hide downstream behind it, which will enable them to rush out and seize prey being bowled along in its grip before returning to the relative tranquillity of the reduced current behind the rock.
Bridges can be good places to fish too, depending on the depth of water. The bridge supports channel the current but, on the downstream side, the supports provide little eddies where the flow is significantly reduced. If the water is shallow these eddies, especially the two nearest to the shore, will be poor to fish with only smaller species likely to be present. If there is a considerable depth of water, then they might well be worth investigating since they will be out of the full strength of the current.

If you look at the diagram again, you will see a solitary boulder breaking the surface. I would work on the theory that a predator was behind it and would certainly target it accordingly. I would also look for the bubble lines, which are often indicative of the edges of the current and which can be hotspots for fish. The reason for this is that food particles are dropped at such points, which are sure to attract fish at some point in time.

As the character of the river changes, becoming deeper, so too does the mix of its denizens. With a good range of cover and variety in depths established, predators such as pike and perch become present in ever greater numbers, as does the range of coarse species. You will still catch the occasional trout but generally these are more concentrated in the shallower, cleaner waters upstream.

Having said that, though the species mix has altered, features will still work in much the same way. Pools, for example, where the river fills a deeper bowl before continuing on its journey, can be very productive. The current slows down a little and food particles are dropped where the fish expect to find them. This means that many species often take up position in such pools. Where they are predators, numbers of smaller fish may be reduced but, where predators are low in numbers, they can fish very well indeed.
Weir pools are often good places to fish for both predatory and prey species. The predators follow the silver fish – wherever there are large shoals of silver fish, pike, in particular, are sure to follow – with the back eddies offering good supplies of food out of the main grip of the current.

Bankside vegetation and places offering cover for predators will all be worth investigating. If you are after predators, look for places where they can ambush their prey while, for prey species, look for places where they have a chance to either flee or hide. Predators and prey will often seek out places that are difficult to reach - under an undercut bank, under a weed mat, under an overhanging tree branch, at the bottom of a deep hole, or behind a rock in fast water. All these places offer both feeding opportunities and shelter from predators. Bear this in mind, use your eyes and your wits, and you will not go too far wrong.
Module 1: Fish Biology
Module 2: Invasive Species
Module 3: Fish Diseases
Module 4: Topography - Lakes
The Sea
Module 5: Angling and Mental Health