The NH DES
has an article about lake foam. Here is part of it.
The foaming of surface waters on lakes is not a new phenomenon. It is a natural process that has been going on for a long time. Foam is created when the surface tension of water (attraction of surface molecules for each other) is reduced and the air is mixed in, forming bubbles. Man-made agents can also reduce surface tension. All lakes contain organic matter, such as algae and plants, and when these decompose they release cellular products (surfactant) into the water, which lessons the surface tension. When the wind blows, the waves on the lake agitate this surface agent, thus transforming it into sudsy white foam. Currents and boats also mix air with the organic compounds present in the lake to produce foam.
While the acid rain creates problems for the lake, it also helps to keep the zebra muscles away. The acid makes it hard for them to form calcium shells. I believe the rain has become less acidic since the steel mills shut down, but coal-fired power plants still contribute acid to the air upstream. The NH DES
also has an article on acid rain and lists some water bodies with impact. Lake Winni is not on the list, but it probably should be.