These clouds usually appear after heavy run-off in the spring or following a long, hot spell in the summer. However, concentrations of this form of algae only in specific areas may indicate a local pollution source, such as a contaminated stream or failing septic system. If a lake develops this type of algae around the entire shoreline, it may be the first indication of a phosphorus problem in the entire lake. Foam along the shore probably does not indicate pollution from laundry waste. Virtually all detergents today are a biodegradable form which is easily broken down by bacteria.
Most foam is natural.
Foam is created when the surface tension of water is reduced and air is mixed in, causing bubbles. Many natural organic compounds will reduce surface tension, including those from decomposing algae and fish. In a lake, these organic compounds are mixed with air by wind and currents to produce foam. Large quantities of foam are often found on windward shores, coves and in eddies. Natural foam has a somewhat earthy or fishy aroma.