Seawater contains dissolved salts, proteins, fats, dead algae, detergents and other pollutants, and a bunch of other bits and pieces of organic and artificial matter.

Sea foam forms when the ocean is agitated by wind and waves. Each coastal region has differing conditions governing the formation of sea foams.

Algal blooms are one common source of thick sea foams. When large blooms of algae decay offshore, great amounts of decaying algal matter often wash ashore. Foam forms as this organic matter is churned up by the surf. 

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Most sea foam is not harmful to humans and is often an indication of a productive ocean ecosystem.

However, it can be exposed to high concentrations of contaminants in the surface microlayer derived from the breakdown of algal blooms, fossil fuel production and transport, and stormwater runoff. These contaminants contribute to the formation of noxious sea foam through adsorption onto bubbles. Bubbles may burst and release toxins into the atmosphere in the form of sea spray or aerosol, or they may persist in foams. Toxins released through aerosols and breaking bubbles can be inhaled by humans. The microorganisms that occupy sea foams as habitat have increased susceptibility for contaminant exposure. Consequently, these toxic substances can be integrated into the trophic food web.

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Scientists studying the cause of a seabird die-offs off California in 2007 and in the Pacific Northwest in 2009 also found a soap-like foam from a decaying Akashiwo sanguinea algae bloom had removed the waterproofing on feathers, making it harder for birds to fly. This led to the onset of fatal hypothermia in many birds.