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What causes the surface of a lake to suddenly change texture. More specifically, what causes short wavelength water waves to dissipate in certain regions of a body of water with fairly sharp transition between regions with short wavelength waves and those without?

Example of water texture transitions

I took a kayak out on lake Michigan (not pictured) and paddled out to a line of transition between water textures. I was about 0.5km from the shore in water much deeper than the wavelength of the surface waves (>2m; longer than my paddle). The air was still, with almost no detectable wind. The water was clear, and I could see at at down to at least the length of my paddle (2m), and there were visibly no fish in the water. To my left the water was rough, with both short wavelength waves (1-5cm) and long wavelength waves (20cm - 1m). To my right, there water was smooth with no visible short wavelength waves but the same long wavelength waves. The transition between the two regions was about 4 meters wide, and both the smooth and rough regions cover very large areas with apparently consistent wave texture within them. It's as if something was low-pass filtering the waves, and I have no idea what it could be. What causes that?

(Neither the smooth nor the rough region featured speckled interference waves like those here: https://www.youtube.com/watch/?v=1dLK6pYEiDA)

Here's some stock photo of the effect: stock photo of the effect: enter image description here


marked as duplicate by Emilio Pisanty, heather, Jon Custer, Yashas, John Rennie Jul 26 '17 at 6:03

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  • $\begingroup$ Possibly a ridge or trench under the surface? $\endgroup$ – probably_someone Jul 25 '17 at 19:21
  • $\begingroup$ I very much doubt ridges and trenches since this is a pretty common effect that I've also seen on small shallow lakes, and also the location of the transition region slowly moves. $\endgroup$ – Schroeder Jul 25 '17 at 20:42
  • $\begingroup$ The wave patterns are large uniform areas of simple mixtures of sinusoids of different wavelengths, not speckled or turbulent waves, nor patterns consistent with upsweeping or convection. The effect also occurs when there is almost no perceptible wind. Speckled interference occurs in small areas under heavy gusts. $\endgroup$ – Schroeder Jul 25 '17 at 20:44
  • $\begingroup$ I'm anticipating a solution something like a non-linear dissipative interaction with the air or other waves that preferentially dissipates short wavelengths. Non-linear because it's a sudden transition; water-air or wave-wave because there's nothing else around. $\endgroup$ – Schroeder Jul 25 '17 at 20:49

In placid waters the surface of water is like a rigid mirror. The image of light source is a single point.

Due to disturbances by wind or fish or large rocks submerged in water a lot of concentric circles are set up (like it is for a single stone) and propagate, their amplitude dies down with distance. The reflecting surface is no more like a rigid mirror. There are many tiny mirrors as each wavelet has a a lateral face inclined at a small angle to the lake surface serving as a tiny mirror surface is interposed between light source and eye of observer.

The sources of disturbances ( the above and water depth) are numerous at the bank as seen in photo compared to nearby areas of water surface. The resulting effect is perhaps what you see.

enter image description here

  • $\begingroup$ This answer is very hard to follow. $\endgroup$ – JMac Jul 25 '17 at 19:42
  • $\begingroup$ No, you need to clean up the wording. It's very hard to follow (in my opinion). $\endgroup$ – JMac Jul 25 '17 at 19:48
  • 1
    $\begingroup$ Tried improving it $\endgroup$ – Narasimham Jul 25 '17 at 20:04
  • 2
    $\begingroup$ Thanks for the attempted answer, but I can tell you that this is not an optical illusion. I physically visited both sides of such a transition in surface texture and observed the waves on both sides 20 cm from the water. The short wavelength waves are real on the rough side and the smooth side is also physically smooth. Also, the effect occurs in the absence of rocks, fish, or perceptible changes in wind. The water texture goes from rough texture that's apparently uniform over large areas to apparently smooth over large areas with a very narrow transition region that slowly moves. $\endgroup$ – Schroeder Jul 25 '17 at 20:20
  • $\begingroup$ No, not an optical illusion. Last para mentioned is a physical relation between wavelength and water depth, and there is a critical depth demarcating the zones at transition. $\endgroup$ – Narasimham Jul 25 '17 at 20:35

It is most likely a very gentle breeze, too faint for you to perceive but strong enough to create ripples on the surface of the water.

In this video you can see the same effect, even if this time the wind is quite strong (and indeed you can see the ripples on the surface of the water moving quite fast).

(If I may add a little personal anecdote from my scarce sailing experience, I remember that whenever we went out in days without much wind we would constantly be looking for these ripples on the water, because it was there that we would have found some wind.)


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