Why does foam form on lakes, rivers, and streams?
Plants, algae and cyanobacteria inhabiting watersheds and surface waters produce many organic compounds. Some of these compounds are surface-active agents or surfactants, as they are commonly called. Like soap, surfactants lessen the surface tension of water. Diminished surface tension allows air bubbles to persist at the water’s surface. Vigorous mixing of surface water by waves, water currents, rapids and boating activity generates bubbles that persist and build up as foam. In lakes, reservoirs and ponds, foam collects along windward shores or may form long, evenly spaced lines, called “windrows”, in open water. In rivers and streams, foam is often found downstream of rapids, in back-currents (eddies), or below waterfalls and dams. While mostly natural, foam can be caused by synthetically produced surfactants released to surface waters. Natural foam typically appears off-white to brown in colour and smells like fish or earth, whereas foam resulting from pollution such as detergent, i
