How to find trout

Having an intuitive understanding of where trout will be lying is key to a successful day on the water, advises Tobias Coe

Knowing how to ‘read the water’ when you are trying to find trout is a skill that 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 which you can use to build a solid foundation of the necessary knowledge. (Read our guide to the top 10 trout rivers.)

Make like a trout

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

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.

Where will the trout be?

Larger fish tend to occupy locations where a regular supply of food 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. (Read this piece on how to catch big trout.)

My observations 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 difficult 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 look for rising fish or read the water to determine the likely spots in which a fish might be holding. Look 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. (Read fishing for early trout.)

Bubble line

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

The presence of cover is critical for trout. Even apparently small nooks and crannies can hold big fish. 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. (Read The Field’s top 10 trout flies.)

Deep water

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.

Speed

A good number of my best trout from UK streams have come from specific spots; 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.

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, 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 here, 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.

Spectacular takes

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.

This article was originally published in 2012 and has been updated.