Foam on rivers can occur from a large amount of organic matter in the water and heavy turbulence from snowmelt.

Foam in rivers, lakes, and streams are often the result of natural processes, not necessarily environmental pollution. Foam can be formed when the physical characteristics of the water are altered by the presence of organic materials in the water. In the spring there is a higher level of organic matter in the water from the decomposition of plant material. When the plant matter decomposes, the oils in the plant cells are released and float to the surface where the turbulence of flowing water adds air into the organically enriched water which forms the bubbles.

Foam can also be caused  by human activity such as high runoff of phosphates from detergents. Herbicides can contribute surfactants ( substances added to enhance adhesion) to runoff which can also add to the foaming.

The amount of foaming is influenced by several factors:

• Wind direction or turbulence: Natural foam occurrences along stream banks or beaches coincide with onshore winds. Often, windrows of foam can be found along a shoreline and streaks of foam may form on open waters during windy days.
• Natural occurrences in rivers can be found at turbulent sites such as waterfalls and rapids.
• Proximity to a potential pollution source: For example, the presence of silt in water, such as from a construction site can cause foam.
• Composition: A higher presence of decomposing plants or organic material in the water.

How can I tell if foam is from human activities?

Natural Foam

• Feeling: Natural foam is usually persistent, light, and not slimy to the touch.
• Color: Natural foam is usually light tan or brown, but can be white.
• Odor: Natural foam has an “earthy” or “fishy” odor.
• Presence: Natural foam dissipates fairly quickly when it is not agitated.

Foam from Human Activity

• Feeling: Has an oily or slimy feel.
• Color: Usually white in color.
• Odor: May have a “fragrant” or “soapy” smell.
• Presence: Foam persists over a longer period of time.