Reading the Water, Part One, Introduction.

No, this blog post is not about a magical river flowing from the headwaters of the Unicorn Mountains, and if you learn it’s secret language, you could read a story about a magical voyage long ago; rather, it is about knowing where fish can be located within a stream based on observable hydrological and structural characteristics.

As a child learning to fly fish, I was always told that being able to “read the water” is an essential skill for an angler's success. At the very least, understanding the fluid dynamics and structural characteristics of a stream can lend the angler the ability to find fish within a given location. 

From the age of ten onward, I dedicated myself to learning about where fish like to dwell within the dynamic world of moving water. I recall sitting in the passenger seat on long drives into the mountains looking at the streams along the road. “Look at that spot; that ought to be a good spot to fish,” I would say, when I identified what looked like a fishy looking fluvial characteristic. Sometimes, I would beg my parents to stop and let me out so that I could at least make a couple of casts in another fishy looking spot just to see what would happen. I always brought my fly rod with me on family road trips into the mountains with an optimistic hope that a lunch spot would afford me at least a few minutes to practice my fly fishing skills.

When I was 42, I left my previous two careers in favor of pursuing my fisheries biology degree. I spent a summer working as a stream surveyor for the United States Forest Service. Because I had so much previous experience being able to locate fish in a stream environment, I was tasked with conducting stream snorkeling surveys, looking for coho and bull trout. I later learned more scientific terms for defining different stream classifications and hydrological features both in school and on the job. I now have a language I can speak for describing fluvial fish habitat.

I was scouting new water today while taking a bank side stroll with my wife. As we walked along I mapped out this rather featureless beat I might add to my guiding options. We pressed on hoping to find some water with more definition that would appeal to my fish finding senses. I saw an angler working some completely nondescript water, water that I wouldn’t even string up a rod to fish (see my post about laminar flows). To me, it would be like fishing on the moon. There would likely be fish present in that location, but there is nothing unique about the structure to give one a visual clue as to fish location. I then realized that the angler I observed might not be skilled at reading the water, or his skill set may not be strong enough to confidently fish the water with more defined structure and dynamic currents, like those located just upstream from him.

I often see anglers fishing in water I rarely stop to explore. I used to wonder if these people knew something that I didn't, or if they just were not educated enough about reading the water? I know, after having snorkeled in plenty of water like the nondescript boulder flats I see anglers frequently fishing, that the fish are few and far between in those locations. Perhaps they are happy with the occasional fish that they work so very hard to catch?

It would take me a hundred pages to describe the preferred trout habitat and the techniques to fish each and every one of them. To ease your pain, I will parse this information for you into smaller chunks you can read in small doses. Over the course of the summer we will define specific hydrological features and how fish utilize them. I will try to include as many videos and illustrations as possible, so that I can steer you out of the barren cobble flats with laminar flow into more exciting water full of fish.

I will use a specific language to describe rivers and streams, not only when I am describing fluvial characteristics but also when I discuss benthic macroinvertebrate distributions within a watershed (yawn). Yes, that will be another day.

  • Fluvial: Fluvial is a term used in geography and geology to refer to the processes associated with rivers and streams and the deposits and land forms created by them.
  • Benthic: The benthic zone is the ecological region at the lowest level of a body of water such as an ocean or a lake, including the sediment surface and some sub-surface layers.
  • Thalweg: is a line drawn to join the lowest points along the entire length of a stream bed or valley in its downward slope, defining its deepest channel -- often having the deepest, heaviest current.
  • Laminar Flow: In fluid dynamics, laminar flow (or streamline flow) occurs when a fluid flows in parallel layers, with no disruption between the layers. Observed as smooth even current from bank to bank.
  • Substrate: The composition of the bottom of the stream from sand, silt, clay to stones, cobble and boulders.
  • Embeddedness: The degree to which fine sediments surround coarse substrates on the surface of a stream bed is referred to as embeddedness.
  • Riffle: A riffle is a shallow section of a stream or river with rapid current and a surface broken by gravel, rubble or boulders. Riffles are instrumental in the formation of meanders, with deeper pools forming alternately.
  • Pool: in hydrology, is a stretch of a river or stream in which the water depth is above average and the water velocity is quite below average. A pool must extend from bank to bank. A side pool does not extend from bank to bank but to the side with faster water defining one side if the pool. A side pool will generally have a current seam and back eddy characteristics. 
  • Current Seam: the parallel junction between two distinct current speeds as they slip past each other.
  • Foam Line: Where bubbles gather in specific patterns along the length of current as defined by that current.
  •  Pocket Water or Pocket Pools: Small bank side pools outside of the Thalweg that are defined by and protected by boulders that cannot be technically defined as a pool.
  •  Wetted Width: the width of a body of water as described by the current water level.

Up Next: Current seams and bubble lines. What do they mean?