heronblu,
I'm glad you brought this phenomenon up. It's something we see on the Great Lakes and I was dicussing it with a friend a few weeks ago as we crossed the Mackinac bridge. Neither one of us knew the cause of the slicks which have everything but the kitchen sink in them including lots of terrestrial insects which the steelhead feed on. In fact these things are sometimes a magnet for steehead. Thanks Bob for explaining the dynamic behind this phenomoenon.
