Sea foam, also called ocean foam, beach foam, or spume, is a natural phenomenon that occurs in turbulent waters. It is a lathery substance composed of dissolved organic matter that floats on the surface of water and gets accumulated at or near the shore.

Although the foam is generally non-toxic, swimming in waters with thick sea foam can be very dangerous. Inhaling sea foam can cause you to choke and makes breathing very difficult. In some instances, storms can create layers of sea foam that are well over a foot thick. On May 11, 2020, a group of five experienced Dutch swimmers were caught in a thick morass of sea foam and drowned.

Photo "Sunshine foam" by deeuutee is licensed under CC BY-SA 2.0