Cappuccino Coast, Cape Town, South Africa

Sea foam, ocean foam, or beach foam is a type of foam created by the agitation of seawater, particularly when it contains higher concentrations of dissolved organic matter (including proteins, lignins, and lipids) derived from sources such as the offshore breakdown of algal blooms. These compounds can act as surfactants or foaming agents. As the seawater is churned by breaking waves in the surf zone adjacent to the shore, the presence of these surfactants under these turbulent conditions traps air, forming persistent bubbles which stick to each other through surface tension. Due to its low density and persistence, foam can be blown by strong on-shore winds from the beachface inland onto sidewalks and streets.
Hazards
On rare occasions large amounts of sea foam up to several metres thick can accumulate at the coast and constitute a physical hazard to beach users, through concealing large rocks and voids, storm debris and, in northern New South Wales, even sea snakes.