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Water's Impact on Color

by: David Coulson 4/8/2013

In my previous blog, “The Eyes Have It,” I suggest that understanding what fish see is useful to anglers.  Fish sight is an extraordinarily complex subject. It’s likely no one will ever fully understand what fish actually see. Even if we could see the image that the fish’s eye transmits, we still wouldn’t understand how a fish’s brain processes that information.

Fish have eyes similar in structure to ours, including the light sensing components, rods and cones. This allows us to make assumptions on what information is transmitted to the fish’s brain. Rods are extremely light sensitive and responsible for vision under low light conditions.  However, rods are unable to differentiate color.  We see primarily black, white, and shades of gray after sunset.  Thus, we conclude it is probably the same for fish.

Cones are sensitive to color. Humans have three types of cones sensitive to blue, green, and red, whereas trout have four and are thought to be sensitive to UV light. Bass only have two types of cones (according to one source) which are sensitive to green and red.  That suggests bass have trouble distinguishing between shades of blue, and some studies indicate that to be true.

Besides understanding eye structure, we need a basic understanding of how water affects light. Water acts on light in two ways, first like a filter and second by scattering light. Additionally, particulate matter (water that fish live in isn’t pure) further absorbs, reflects, and scatters light.  It’s rather obvious that looking through water is far different than air.  For example, if red light is filtered out in a room, a red object would appear as shades of gray or black.  It wouldn’t matter that we could distinguish reds, under those conditions where a wavelength of light doesn’t exist that color doesn’t exist to our eyes.  This situation occurs underwater. 

In clear water, the longer wave lengths are absorbed (filtered out if you will) first, reds and oranges.  With greater depth yellows, greens, violets, and finally the blues are the last light to go.  Simply, if you go deep enough in the ocean light ceases to exist.

However, most of the waters we fish are not very pure.  Even “clear” waters often have a greenish tint to them due to plant life. Consequently, those “clear” waters absorb the violets, blues, reds, and oranges faster, leaving just the greens and yellows.  In these circumstances it’s rare for fish to see beyond 50 feet, and their world has a greenish background.

In stained/muddy waters most of the shorter wavelengths get absorbed leaving the reds and oranges.  In these cases light penetration may only be a few feet at best.  In all situations, light/colors penetrate their deepest under clear skies, calm winds, and high sun.  The further from that situation, the less light/color penetrates the water.

OK, what does that mean to you, as an angler?   Maybe very little, if you always fish clear waters shallow on bluebird days. But if you’re fishing deep, say 15 to 20 feet on a cloudy day with red or orange lures, they likely appear brown or black to the fish. Does that mean they won’t catch fish? No. What it does mean is that changing out a red lure that isn’t working for an orange lure or black lure of the same type under those conditions is probably a waste of time.  Or when fishing muddy water, a foot or so of visibility, in 10 feet of water, color probably isn’t going to matter much, as other than reds and oranges fished shallow, most colors are going to look much the same.

Does color matter? My thoughts are yes.  But how much depends on the water color, water clarity, brightness of the day, and how deep you fish.  Shallower, clearer, and brighter conditions are those where color can have a large impact. Deeper, murkier, and dimmer conditions suggest color is probably far less important than contrast.

Contrast being the ability to stand out from the background.  In simple terms, looking into the light dark objects show up best (that includes at night) with the light behind us (and bright conditions) bright objects will show best.

I didn’t address florescence and phosphorescence, but I will later, as they are important in terms of colors and objects being visible when normal materials are not.  Further, I want to discuss contrast in greater detail.  

Blog content © David Coulson
Member comments
Bigbasswanted, CO   4/9/2013 8:42:30 PM
I was pondering the meaning of color just the other day. Thanks for the article. So in darker tinted waters, go with a darker color?
H the yeti, CO   4/9/2013 11:53:29 PM
Thanks. I will wait for your next post before asking my questions about artificial light.
David Coulson (Flyrodn), CO   4/10/2013 6:29:27 AM
The general rule for best contrast is dark water, dark colors, light water, bright light colors. The reasoning is the dark color produce the best silhouette as the fish looks toward a dimly lite sky/surface. Whereas went the water is clear, and bright sun light the colors are reflected making them easier for the fish to pick up. Remember these are general and do not account for lure action, sound, pressure waves, or scent. All fodder for future discussions.
Bigbasswanted, CO   4/10/2013 10:33:16 AM
Thank you
JKaboom, CO   4/10/2013 8:48:24 PM
Good write-up :)
David Coulson (Flyrodn), CO   4/11/2013 9:01:03 AM
Thanks for the compliments. This has been, and continues to be a learning process for me. Reading, studying, and thinking about this topic has me wanting to do a bit of expermentation. Once I get moved into my new place, I'll have a full room dedicated to fly tying. I hope to set up a few things so I can simulate underwater conditions (using light filters) to see how some of my creations appear. May even install an aquarium. We'll see.
David Coulson
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