Foam is usually harmless. In fact, only 1 percent of the foam you see on a waterbody is the actual foaming agent; the rest is air and water. However, excess foam is sometimes the result of too much phosphorus in the water. Although phosphorus is an important plant nutrient, it is not found abundantly in nature and too much of it is indicative of pollution from human activities. Excessive phosphorous can result in nuisance algae blooms, fish kills due to low dissolved oxygen from decomposition processes, and irregularities with the water's taste and odor.