Cappuccino Coast, Cape Town, South Africa

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.
Where polluted stormwater from rivers or drains discharges to the coast, sea foam formed on adjacent beaches can be polluted with viruses and other contaminants, and may have an unpleasant odour.
If crude oil discharged from tankers at sea, or motor oil, sewage and detergents from polluted stormwater are present, the resulting sea foam is even more persistent, and can have a chocolate mousse texture.
If the foam forms from the breakdown of a harmful algal bloom (including those caused by some dinoflagellates and cyanobacteria), direct contact with the foam, or inhalation of aerosols derived the foam as it dries, can cause skin irritations or other respiratory discomfort.