What is reading water?
At the most basic level, it is the process by which an angler determines where fish are most likely to be. By assessing a number of variables, it is possible to figure out which parts of a river have the highest percentage of holding fish. But what becomes an intuitive process after years and years of fishing isn’t necessarily innate. There are some spots, such as deep emerald pools, that do call out to anyone with a rod. Others, such as seams, undercut banks, and riffles, require a bit more experience and discernment.
Again, reading water well includes factoring in countless variables. Prominently, a fish’s desire to eat and be safe must be taken into account. Applying those criteria to a creek, pond, or coastline is where the work comes in.
A simple, fourfold method can help anglers read water. This top-to-bottom approach is a quick and comprehensive way to survey a stretch of fishable water.
Cover
An underappreciated aspect of any aquatic ecosystem is what is above. Overhanging limbs and extended banks draw fish in for the shelter and food that they provide. Predators, such as raptors and people, are less likely to get at a fish that has something above it. If there so happens to be some ants or mulberries that fall in with any frequency, all the better. It can be touching the water or even twenty feet beyond the surface and there will be in impact from cover.
Current
For the fly fisher, there is not an aspect more vital to understand than current. Surface currents, in particular, are the diagnostics for so many choices the angler must make. Chop may indicate some of structure or bottom contours if they can’t be seen or felt. Slick water against a quicker flow is called a seam: these spots are perfect for animals that limit caloric expenditure (finning in slower water) while taking advantage of the greatest caloric intake (what is brought by in faster water). Plus, currents determine things like leader length, tippet diameter, and casting/mending dynamics.
Structure
Even a bowling-ball sized boulder in a large river can be structure. It creates a calmer pocket compared to the surrounding water that smaller organisms can utilize. Sportfish will go to structure for the food, and they will stay there for the same benefits. Stumps, boulders, and even man-made debris will cause fish to congregate within and downstream. As was already mentioned, larger structure can impact currents and create challenging presentation puzzles that must be solved to get a fly before fish.
Bottom
Depth is essential for safe wading and effective fishing. Changes in depth are worth targeting. Shallow to deep or deep to shallow both present opportunities. Similarly, channels through rivers or between pools are paths worth sending a fly along. Along with knowing there is a probably a fish in a particular spot, understanding depth and flow will help determine weight, how far upstream to cast, and even where you should position yourself.
While only a cursory explanation, taking these four variables into account gives the angler a composite picture of a habitat. Coupled with some fishing know-how and a rudimentary grasp of fish behavior, and there should be some good results if executed properly.