We're making our way through all of the data available and hope to have most metro lakes up soon. Surface tension can be reduced by both natural organic compounds and by man-made soaps and detergents. In a lake, wind, currents, and boats mix air with the organic compounds present to produce foam. The foam will frequently form parallel streaks in the open water, caused by wind-induced surface currents. It will also collect in large quantities on windward shores, coves, or in eddies.
Natural foam has a somewhat earthy fishy aroma.
Detergent foam in contrast will have a noticeable perfumey smell. Scum, an oily film, or yellow-green dust on the surface of a lake make it looks contaminated but, in most cases, nothing is wrong. In fact, something natural is probably occurring. An oily film in mid-summer is most likely caused by insect cases that were concentrated along the shore by wind after a hatch. Insects can hatch any time from ice-out into September.