A fundimenal attribute of any successful angler is the ability to read the water and determine where to place the fly, lure or bait at the end of one’s line. For the trout angler fishing a dry-fly, this is often easier when casting to a rising fish, as the fly “simply” needs to be placed upstream of the visible fish. However, when prospecting with flies rather than casting at sighted fish or a fish that’s rising sporadically, having an intuitive understanding of where fish will be lying is key to a successful day on the water.
For most of us, the bad news is that such knowledge can take a lifetime to build up, from days and weeks on the water. It is a gradual, incremental process, akin to adding pieces to a mental jigsaw puzzle. The good news is that there are a few key building-blocks that can be used to form a solid foundation, on to which further information can be added over time.
Make like a trout The most important prin-ciple is, in essence, very simple. Trout have two main concerns throughout most of their lives. These are: 1) to consume enough food to sustain themselves and grow while minimising energy expenditure, and 2) to avoid becoming part of “rule one” for another, be it a larger trout or another predator. So, to increase your chances of connecting with a trout, it helps to think like one. Trout, particularly the larger individuals that we are more interested in catching, tend to sit in spots with a reasonable source of food, and close to some form of cover.
In the case of a ready supply of food, larger fish tend to occupy locations where a regular supply is swept to them. The precise location can be hard to determine, except in very clear streams – the world of trout is one of micro-currents and complex flow dynamics. My observations and those of good fishing friends on clear streams across the world show that a fish in a feeding lane will often hold station, almost imperceptibly moving to intercept nymphs and other invertebrates as they are swept down to it. This behaviour can be dif-ficult to observe in anything except a gin-clear stream, with an elevated view through the water surface down on to the fish.
In the absence of such conditions, it is ne-cessary either to look for rising fish or read the water to determine the likely spots in which a fish might be holding. Look, therefore, for points when two flow streams come together or when the flow is channelled into a narrower flow-line. Trout will be sitting in such points and mopping up any food items floating down to them, both below and above the surface.
A highly visual example of such a situation is the so-called “bubble-line”. This is created where bubbles – formed on the surface, as water splashes over a cascade or drop – are focused downstream by the flow into a single line that runs parallel with the river flow. The surface bubbles provide us with an easily readable clue as to what is going on under the water. Trout often hold in these bubble-lines, waiting for food to be washed down to them, and several fish may hold in a single bubble-line, one behind the other. It is worth fishing such areas carefully, directing one’s first cast to the downstream end of the bubble-line and methodically working upstream.
Cover me, I’m going nowhere Just as a regular supply of food is important, the presence of cover is critical for trout. Even apparently small nooks and crannies can hold big fish. The instinct many of us have from when we started fishing to cast to cover is well guided. Make sure you cast a fly under all those overhanging branches, any undercut rock shelves and large rocks midstream that break the flow. The latter can be particularly important and good trout are often found sitting midstream in what seems like a fast current, tucked in a small flow depression behind or in front of a rock. My best fish from a trip to the River Usk last spring came from such a spot; it took a nymph drifted through a swift pool towards a rock sitting right in the middle of the flow. The fish intercepted the nymph right in front of the rock in a classic feeding lie, using the cover to keep out of sight and out of the main flow.
Plumbing the depths The all-important cover does not necessarily have to be of a physical form as we tend to think of it. Deep water provides a cover all of its own. Some of the biggest trout I have ever seen were sitting at the bottom of incredibly deep pools in crystal-clear Icelandic streams and holding station in a position out of harm’s way yet fully visible. Such behaviour is not limited to fish in foreign waters. It is no coincidence that big trout are sometimes taken by salmon anglers swinging flies through deep pools and salmon lies.
Big trout often undergo a diet shift as they get larger and become more piscivorous; after all, there’s a lot more protein in a salmon or trout fry than a mayfly nymph. They become more predatory and often take up residence in deep pools, coming out to take any bite-sized prey that ventures near. Some friends of mine take advantage of this behaviour using a technique that isn’t common here but has a following in the US and Canada. Swinging big streamers through deep pools has yielded some seriously big trout – up to sizes that would rarely be encountered using “standard” trout-fishing techniques. It isn’t everyone’s cup of tea but is worth trying if you want to tempt an outsized trout from your local stream.
A matter of speed A good number of my best trout from UK streams have come from specific spots that I used to have little interest in fishing during my first forays with a fly-rod. These are the high-velocity waters that form a cascading run. As long as there is a reasonable water depth, there is a fair chance that a good trout resides there. The turbulent water overhead creates cover of sorts, so the trout feels secure. As we look from above, the flow looks too rapid for a fish to hold in. However, from a trout’s perspective, the reality is quite different.
There are several factors at play here. The first is that often the water near the river-bed is moving much less quickly than at the surface, evident in the schematic drawing of a typical turbulent trout lie (top), where I caught a good fish last summer. Water velocities down through the lie were measured using a flow-meter and clearly illustrate that there is an area of low velocity near the bed of the river. This is most noticeable where the river-bed drops off, and it was here the fish was holding.
The second factor relates to the way in which trout maintain their position against the flow. By utilising their pectoral fins and the localised differences in flow, they are able to hang, almost still, in a flow-line of ideal velocity, just as a hawk hovers against a headwind.
The final variable is the swimming ability of trout, and fish in general. For a given species at a given temperature, larger fish swim faster, both in terms of their maximum and cruising speeds (as well as the flow against which a fish is able to “hover”). This largely intuitive fact is presented in a simple graph (below left) calculated from scientific equations that relate swimming speed to temperature and fish size.
These factors combine to enable trout to sit in a lie that may appear, at first, simply too fast and tumultuous. Furthermore, the disparity between the flow a fish is actually sitting in and the flow over its head serves to bring more food to the fish than would be the case otherwise. As a benefit for us, takes from fish in such spots can be spectacular, with dry-flies snatched from the surface with smash-and-grab force.
Similar elements are important for trout holding station in shallow riffles. While these can look simply too shallow to hold good fish, it is surprising quite how many fish you might find. The turbulent water overhead creates a form of cover, as in a cascade, and trout are able to shelter behind even relatively small stones, which break the flow. In addition, the turbulence of the riffle turns over and aerates the water, something that becomes more important during the summer, when flows are low and water temperatures high.
Rules are there to be broken Some surprisingly large fish, however, clearly don’t seem to read the rule books and can be in very unexpected locations. Catching them, therefore, relies on seeing them, either directly or when they break the surface to take a fly. Take note of the location of a single fish breaking the surface with a careful sip, even if in an area of shallow, still water. Don’t flock-shoot and go in after such fish with several prospecting casts. Instead, wait until you are sure where the fish is sitting. As long as the fish is undisturbed and hasn’t detected the angler sneaking up on it, and as long as cover is close by, it should take a well-presented fly.
Even though I have had several good fish out of such spots, it can still be a little unnerving dropping a fly upstream of a fish that has risen in a spot that just doesn’t look very “trouty”, only to have it sucked from the surface by a good fish that then cartwheels into the air or shoots upstream through the shallows.
Reading the water is a real art but one that is worth taking the time to master. Building a mental picture of where fish sit, and why they sit there, really helps when approaching both home waters and rivers farther afield, and deciding exactly where to cast one’s fly.