Being a director on the board of a local resource conservation district (RCD) with a salary of $0 per year is a lousy way to amass a financial fortune, but there is an upside. You get to work with very talented folks doing really cool environmental projects.
Way back in 2015, the Santa Cruz County RCD partnered with a private landowner to install some fish-friendly structures in a local creek. This waterway still has a run of steelhead, though the numbers are depressing. In 1959, the annual run was estimated at 11,500 fish. By 1996, it had dropped to 100, a number that looks like a guesstimate to me. No one knows how many steelhead make it back these days, but evidently some still do. The landowner wanted to ensure the few fish that do return would have a place to spawn and that their progeny would have somewhere safe to grow. He asked the RCD to help make that happen.
In this case, the structures were the root wads and trunks of large trees, strategically placed into the creek. The technical term is large woody debris (LWD). Dick Galland’s piece on Hat Creek (“The Good Fight,” California Fly Fisher, May/ June 2018) describes them, so I won’t go into details. Suffice it to say that LWDs, when properly sized, located, and secured, help create spawning and rearing habitat for steelhead and their young. I joined RCD staff on a trip to the site in mid-2017 to see how the structures had fared after the wettest winter on record. While the creek had cut a new side channel and moved its banks in several locations, the LWDs were still in place and functioning as designed.
While the view from above was good, I wanted to see how things looked from the steelhead’s perspective. I decided against donning a wetsuit and diving in, because that didn’t seem like a particularly safe way to examine a tangled mass of submerged timber in a strong current. Instead, I mounted a GoPro camera on a 16-foot DIY “selfie stick.” I shot almost an hour of 4K ultrahigh-definition video, hoping to capture as much detail as possible.
My preconceived notions of how things should appear to a steelhead were based on photographs and diagrams I had seen in books on fishing and biology. These books described how the optics of the underwater world are dominated by Snell’s window and the mirror. The window is a circle of light located directly above a fish into which things above the water are compressed and visible to the fish. Trees, sky, and bumbling anglers all appear in the window. Photographs taken with a fish-eye lens also produce this bizarre visual effect. The surface of the water beyond the window is called “the mirror,” because it reflects everything below the surface. Unlike the window, anything above the surface is invisible in the mirror.
Looking at the videos, I couldn’t help but notice that the static images and diagrams provided by the books were way too simplistic. A fishy-looking riffle downstream of one of the LWDs was fascinating. The mirror was a fast-moving mosaic of complex morphing geometrical shapes. Ripples and eddies fractured the window, blending much of it into the mirror. None of the textbooks or fishing manuals had described such a colorful and chaotic scene.
This made me wonder if the subsurface optics also would be more complex in clear, slowly flowing waters. Places such as the Fall River and Hat Creek came to mind. These are waters that will test the skill and sanity of any angler. Anyone who has fished such waters knows that larger trout will often bolt the second you cast or when your line lands on the water.
Clearly Green
By midsummer, the San Lorenzo River in Santa Cruz County runs slow and clear. An exploratory trip this July revealed ideal filming conditions on a section just outside of town. Nestled below second-growth redwoods and sweeping willows was a gravel-bedded run. The water had a glass-smooth surface and was so clear that standing on the bank, you could see items as small as a split shot on the gold-colored streambed. I found a spot that was just over two feet deep, placed the camera on the bottom, and started filming.
My first reaction upon viewing the videos was one of slight disappointment. The mirror reflected the streambed, while a roundel of green and blue marked the trees and sky in the window — exactly what I had seen depicted in magazines and books. Then I noticed that the streambed and its reflection in the mirror had a decidedly green tint. A few feet upstream of the camera, the mirror and the streambed disappeared into a solid wall of green. The “clear” water was clearly not clear. This got me thinking about how fly lines appear to the trout. “Time to do some experiments,” I thought.
Shooting Lines
I contacted the folks at Scientific Anglers, Orvis, Cortland, and RIO, told them what I was up to, and asked if they would send me some sections of lines for testing. To my delight, they all responded, and within a couple of weeks, I had about two dozen pieces of line in a wide range of colors. Back at the river, each section of line was looped onto the front of a 5-weight fly line and gently cast upstream of the submerged camera.
For the first video run, the camera was oriented upward at 45 degrees, showing the window and the mirror. This is the view a trout would have if it were rising toward a dry fly or shallow nymph. For the second video, the camera was repositioned to shoot parallel to the streambed, showing the mirror and the gravel as it would appear to a trout seeing a more deeply sunk nymph or streamer. I raced home, opened the videos, and got several “Well I’ll be dipped!” surprises.
Line Flash
When it comes to fishing challenging trout waters, one of the main concerns has been the visibility of fly lines during casting. It doesn’t matter if you have the perfect fly and a totally drag-free drift if the fish has already been freaked out by the sight of your line racing overhead. This makes sense from an evolutionary perspective. Trout coevolved with numerous avian predators. Kingfishers, terns, ospreys, and bald eagles all prey on trout. Natural selection would tend to favor fish that got the heck out of Dodge when something flashed above. As far as the trout’s brain is concerned, your fly line could be an osprey.
The issue of line visibility was explored by Brian Clarke and John Goddard in their groundbreaking book The Trout and the Fly (1980). Much of the work for the book was conducted on the Kennet, a chalk stream in southern England. I was lucky enough to fish the Kennet a few times and know just how spooky its trout can be.
In chapter 8, “What the Trout Sees of the Angler,” Clarke and Goddard describe how underwater photography had revealed that brown, green, and white lines were indeed visible during casting, though their findings suggested no color had a significant advantage. They did state, however, that white lines were more prone to flash and that this might suggest darker lines were a slightly better choice. My videos seemed to agree with their findings. The lines were all visible in the window, against either the green of the trees or the blue of the sky, but for most of them, the effect was not particularly dramatic. However, I did test one line that was not available in the late 1970s when The Trout and the Fly was being researched and written. A clear floating fly line was noticeably flashier than the other lines. Closer inspection of one particularly bright section of flash revealed the colors of the spectrum. This meant the clear line was not only reflecting light off its surface, it was also refracting light like a simple lens.
If this sounds a bit far-fetched, you can easily run your own tests. You don’t even need a camera. Just take a clear line (floating or sinking) out on a sunny day. Start with your back to the sun and move the line around. Repeat the process while facing the sun. You’ll notice that when you face the sun, the line flash is very bright. That’s due to refraction.
Lightning Strikes
One thing that jumped out straight away was the way the lines landed on the water. I had naively assumed they would make a series of ripples. Instead, the lines often had sufficient momentum to break through the surface, creating a lightning bolt of silver bubbles that raced across the surface. This effect was quite visible eight feet upstream of the camera. A leader helped tamp down the effect, but did not eliminate it. This alone would seem to support the use of long leaders, finetipped f ly lines, and deft casting when fishing clear waters.
Floating on the Water
Having addressed line flight and landing, I turned my attention to the issue of the line’s visibility as it floated toward the camera. The $64,000 question, posed by countless folks, is “Which color is the least visible to the fish?” Not surprisingly, this subject has spawned a number of theories, which occasionally get debated online. Some “theories” appear to be based on little more than speculation, such as blue lines must be less visible because they would blend in with the sky. Others, such as the preference for dull lines of many Kiwi guides, seem to be based on more reliable empirical evidence. What surprised me was that very few of these theories (if any) are actually based on the view from below.
Clear Lines
It seems logical that a clear fly line floating on the water would be less visible to fish and therefore the most stealthy. Since these lines are almost transparent, they should be better at blending into the background and also create less of a shadow when they pass through the window, though the window is actually far less important for reasons we’ll address later. These advantages should more than make up for any difficulties the angler (or a guide) may have actually seeing the line on the water. As such, a clear floating line should be almost perfect for technical waters. The videos, however, depicted a very different story.
The flash that had been apparent during casting also showed up on the water. Bright spots and bands of silver marked every subtle curve in the line (no line lies totally straight). Unlike the diffuse reflection coming off colored lines, the light reflected off the clear line had a mirrorlike quality. Based on this, I’d probably not make a clear floating line my first choice, especially on a sunny day.
Bright Lines
You have no doubt noticed that many of the floating fly lines currently on the market are quite vividly colored. This certainly helps with things such as casting and mending, where the ability to see the line can be a real benefit. But I suspect there’s also a psychological reason why we buy them. Studies have shown that colors directly affect our moods. Pharmaceutical companies have even found that certain colors make their medications more effective through the famous placebo effect. Based on this, it’s not a big stretch to assume that bright lines sell better because we like them. I must admit that I really enjoy casting a neon orange Scandi head. But what about the trout?
In general, things become more visible when they contrast strongly with their surroundings. A bright object is more easily seen against a dark background and vice versa. You can get an idea of how a line contrasts with its background just by looking at it, but I wanted something more quantitative.
One of the advantages of digital photography is that you can quickly analyze images in a way that Clarke and Goddard simply could not with their old film cameras. You can determine the contrast between two objects by measuring their luminance. The larger the difference in luminance values, the greater the contrast. This is easy to do with photo-processing software.
To start, I measured the average luminance values for the window (210 for blue sky, 140 for trees) and for the mirror (105), since these would be the background against which the lines would be seen by the fish. The brighter lines, with their higher average luminance values (150 to 223), were indeed more visible in the mirror and also against the trees in the window. And not surprisingly, they were less visible against the blue sky, which dominated the center of the window.
Dull Lines
Much like the spooky trout swimming in California’s spring creeks and English chalk streams, New Zealand trout are famous for testing the mettle of any fly fisher. Kiwi guides are well known for having strong opinions about fly lines, with most recommending a dull color. The videos seemed to support the Southern Hemisphere’s dull-line advocates. The lower luminance of the darker lines (120 to 140) made them less visible in the mirror and against the trees, but slightly more visible against the bright blue sky.
The value of actually measuring luminance, instead of just eyeballing it, became apparent with a gray fly line I got way back in 2006. Luminance measurements showed that the line was slightly brighter than peach and blue lines, both of which appeared brighter to my eyes. Perception isn’t always reality.
Window or Mirror?
Bright lines are more visible in the mirror, but less visible in the window, while dull lines are less visible in the mirror, but more so in the window. So what’s more important, the mirror or the window? Many folks have written about the importance of the window, and for good reason. This is where the trout will typically see your fly and tippet as the fish moves in for the kill. If anything looks wrong, the trout will refuse your fly. No doubt you have experienced this. I certainly have. But the window is almost totally irrelevant for fly lines. I imagine this statement may not jibe with what you have read or heard, so let me explain.
Whether a fish will see your fly line floating in the window is dependent on the depth at which it is swimming and the length of your leader. A fish swimming two feet below the surface has a window just over four feet wide. Even four feet down, the window is only nine feet wide. So even if you cast to a fish four feet down and your cast is so bad that the fly lands on the far side of the fish’s window, a typical nine-foot leader means there’s only a few inches of fly line intruding into the window. Most of us cast well enough that a nine-foot leader is plenty long enough to keep the fly line out of the window. If not, the color of your fly line is not the problem — your casting is. What is important is the color of your line in the mirror.
Mirroring the Mirror
As the armed forces, hunters, and folks who fish for savvy trout have known for many years, to avoid detection, you need to blend in with the background. This is true for floating fly lines, too. In clear streams, the mirror is the background. If your fly line is the same luminance and color as the mirror, it will be much tougher for the fish to spot. While things such as water depth, streambed color, and wind can change the color of the mirror, the videos showed this is significant only close to the window. At distances over six feet (which is shorter than typical leader length), the mirror and the underlying water were the same color and quite indistinguishable.
In the case of the San Lorenzo, the mirror color was highland green (Hexadecimal color 003826). The mirror in the creek with the LWDs was avocado green (568203). I suspect some shade of green will be the dominant mirror color in the vast majority of California’s rivers and creeks. A quick check of online underwater images for the Truckee, Trinity, Sacramento, and Yuba Rivers all showed a predominantly green mirror. It’s possible that high-elevation, low-nutrient streams could have more of a blue/green color due to lower levels of suspended and attached algae.
But let’s get real. Fly-line makers don’t produce fly lines based on the hexadecimal system or for specific rivers. So what is the least visible color line you can actually buy for most “clear” streams? I’d suggest you look for Scientific Anglers’ MPX (willow) or their Double Taper (dark willow), Cortland’s Spring Creek or Ultralight (aqua green), or RIO’s Gold (moss). Orvis is currently working on new lines and colors and consequently could not provide specific line recommendations by press time.
Intermediates in Lakes
The unexpected results with the clear floating line made me wonder if clear sinking lines would have similar optics. One of the most productive fly lines you can use in a lake is an intermediate, with clear or clear-camo being popular options. With a sink rate of one to two inches per second, these lines allow you to fish from just below the surface to 5 feet down. If you are patient, you can even count them down to 10 feet or more. They can be deadly during a caddis or Callibaetis hatch and are great for fishing baitfish patterns.
I took four intermediate lines to a clear mountain lake and shot 4K video as they were submerged (in one-foot increments) to a depth of four feet. I shot the video facing into and away from the sun to see if the lines exhibited any reflection or refraction of sunlight. The results were pretty much the reverse of the floating-line tests. The least visible line was a clear intermediate, which had a luminance almost identical to the background and produced no flashes. The clear camo intermediate was almost as stealthy, coming within 14 points of the background luminance, and it also exhibited no flash. Light olive and light blue intermediates produced minor areas of flash and had similar luminance values, which ranged from 35 to 75 points above the background. While I don’t think trout in most lakes are as twitchy as spring-creek fish, these tests would make me more likely to use a clear intermediate.
Trust, but Verify
You may question whether these line-color recommendations are valid for the waters you fish. While I am reasonably confident they will be, it’s pretty easy to run your own tests. Simply get a clear waterproof pouch for your smartphone, submerge it a foot or two below the surface, and shoot some video. You should be able to see the dominant color of the mirror and can choose your line accordingly. If that sounds like too much trouble, see if anyone has posted subsurface shots of fish being released in the river or lake you fish. If you are lucky, the image will show the mirror and the water below. Beware of any shots where the fish looks especially colorful, since this could be an indication that the image has been adjusted with photo-processing software, which will also affect any line in the image.
Lessons Learned
So does line color really matter in clear waters? The answer appears to be yes. Having a line that matches the color of the mirror should go a long way toward helping you connect with bigger, wiser fish. But the color of your fly line is only one factor to consider. I know this is going to irritate the heck out of a lot of folks, but you shouldn’t expect to catch big fish in clear waters if you don’t know how to cast accurately and gently. If you can’t make your line settle softly onto the surface, regardless of its color, expect to spend a lot of time watching terrified trout bolting for safety.
I’ve had a long career in water quality and almost fifty years of fly-fishing experience, but the videos showed me that I really don’t know much about the world that fish inhabit. I suspect the same is true for many fly fishers. Maybe it’s just me, but I find that quite exciting. What else have I got wrong?
