Both dissolved organic matter and pollution reduce surface tension and allow air to become trapped in water leading to the formation of bubbles and foam, especially from wind, rain, waterfalls and rapids. Decomposing organic compound release fatty acids and oils that act like natural soaps, they’re typically off-white/brown with an earthy smell, while detergents, fertilizers, pesticides and industrial waste may produce a more persistent bright white, slippery, chemical-smelling foam.
