Similar "oil slicks" have been discussed from time to time. I couldn't find a good, definitive (i.e. hard technical data on what is really is) thread in the last couple of years, but reportedly proteins from decaying vegetation or iron bacteria (common in high-iron content ground water) can cause an oil slick appearance. I did not see anyone associating fish health problems with this phenomena.

"Live like you'll die tomorrow, but manage your grass like you'll live forever."
-S. M. Stirling
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