Hi Driftless Region FFF,
Will be fishing the Vernon County area this week. I’m wondering if wearing bright colored clothing matters for this area? I ask because I’m generally a fan of bright oranges and blues, so much of my fishing clothing features is this color scheme. I know moving slowly and coming from down stream are most important. And, last time I fished this area around Labor Day during bright sunlight I couldn’t even get within the periphery of fish without them seeing me. So my thought is 1) don’t false cast above the area of stream I’m fishing mainly because the spray puts the fish down, 2) move very slowly, 3) cast from directly down stream so I’m not in the perimeter, and 4) long, 10-12 foot 6x leaders.
You already know the answer.
"last time I fished this area around Labor Day during bright sunlight I couldn’t even get within the periphery of fish without them seeing me."
I would try to match the color of the background and walk low and slow. Low to stay under the 10 degree line of Snell's window and slow because regardless of color, motion to fish means danger.
You may think that fish cannot see you from directly downstream of them, but they can. Even a fish staying in place moves its body from side to side in swimming motion. Although there is a "blind spot" directly behind the fish, that blind spot MOVES during the side to side motion of the fish and there is no place that is not seen from time to time even directly behind the fish. So it is LESS LIKELY that the fish will see you BUT it still CAN see you.
Simply put, bright colors make you more visible so you are making it more likely that a fish will see you. Again it comes down to statistics and probabilities. The probability of you being seen increases with bright clothing and decreases with clothing that matches the background.
As to 15/20 feet being the safety zone, that is really not true. Fish see the outside world through Snell's Window which compresses 180° into approximately 97° The distance you must stay away depends on HOW DEEP the fish is and HOW HIGH you are. The closer the fish is to the water surface and the height of you AND your rod above the ground determines whether you CAN be seen. This assumes a smooth water surface. With riffles, you can get much closer. As you will see in the detailed calculations at the end of my post, at 15 to 20 feet from a fish in clear flat water you will likely be visible unless you are a
reeaalllly tiny person.
Snell's window - Wikipedia
Snell's law means that if you stay UNDER the 10° line from the EDGE of the window, the fish will not see you. The deeper the fish, the larger the window and the further away you must be.
Ever wonder why fly rods are "balanced" to cast 30 feet of fly line? It turns out that at 30 feet from the edge of the window, the 10° line is at 5 feet. It is the
rule of 6
The application is simple but the explanation is complicated.
To apply the principle, I use the
rule of 6.
Divide your distance from the outer edge of the trout's window
by 6 to find how far above the water you can be before being seen. If you are 18 feet way, you need to be lower than 3 feet, at 24 ft, you need to be lower than 4 feet and so on. Simple
The explanation is that when light enters or leaves a water/air barrier it will bend. The next time you are walking next to a clear pool, stick your fly rod into the water and it will look bent at the point at which it enters the water.
Light bends so that when we look at an object in water it will look further away and shallower than it really is. So when you see a trout it is really closer and deeper than it looks to you. That is the bending of light as it leaves the water to your eyes.
When the fish is looking at us through it surface window, light entering the water also bends such that, the light that enters at a narrower angle is bend more. Only the light entering at 90 degrees (directly overhead) to the water surface is not bend. This means that the light that enters from objects at a low angle to the water surface is compressed and distorted. Only when the entry angle is greater than 10 degrees can the object be seen relatively clearly. This is why we need to stay below 10 degrees.
How then does this lead to the rule of 6? It is plain geometry.
Consider the right angle triangle in the illustration below. Suppose the closest edge of the fish's window is at point (a). Angle h-d is 10°. Distance from the window edge is the length of side (d) and the height of the 10 degree line is length of side (h). The tangent of 10° is h/d = 0.1763 so the height you need to stay under is h = (0.1763 ) x d(the distance from the edge of the window). It so happens that the tangent of 10° is about 1/6 or 1.667. Dividing (d) by 6 gives you (h) = the rule of 6.
Notice also in the illustration below that the position of the flying mayfly is shifted closer to the vertical by the refraction of light by the water.
The
depth of the fish also changes the size of the window. In the diagram below I have added arrows for the size of the window and the depth of the fish. You will also notice that the angle of the window from the trout's eye is 97.5°. Half of that if 48.75° which is about 45°. At 45°, the distance = r from the center of the window to the edge of the window is exactly equal to the depth =r of the fish. So we can approximate the the size of the window from the depth of the fish.
The window diameter is 2r or about
twice the depth of the fish.
Note also that the
deeper the fish, the larger the window. That means that the deeper the fish, the closer the edge of the window is to you and the lower you must be to stay under the fish's vision.
The size of the window also compresses the image of the outside world into a very limited space that gets increasingly smaller as the fish gets closer to the surface. You can now understand why,
when the trout is feeding selectively and holding just under the surface, we can get very very close to the fish. His image of us is limited by the window size as well as the 10° line.
Notice that I said you have to divide you distance from the EDGE of the trout's window. How do your figure out where the edge of the window begins? The geometry above indicates that the edge of the window begins at about the same distance from the trout as the depth of the trout.
So if the trout is 5 feet deep, the diameter of the window is 10 feet and the edge of the window is 5 feet from the trout. Because the bending of the light by the water/air interface works in both directions, the actual fish will be deeper and closer than it looks to be. So you need to account for this optical illusion when estimating the edge of the window.
Most often the need to fish downstream to rising trout will be when the fish are shallow and have a very narrow window diameter in slow moving water with complex currents. The down stream approach is needed to get the fly both into the feeding lane with accuracy and free of drag.
Because the window is so small, all of the visual field is crammed into a few square cms. of window. The fish has a harder time seeing a waving rod than if it were deeper and the window larger.
So to answer your question as to whether the fish can more easily detect bright colors, yes, If you have to crawl around on your hands and knees all day because of bright colors, your shirt will soon be the color of dirt and grass so you might as well start that way.
