If you closely look at a glass of water from the ocean, you'll see that it's full of tiny particles. 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. If you shake this glass of ocean water vigorously, small bubbles will form on the surface of the liquid.

Sea foam forms in this way - but on a much grander scale - when the ocean is agitated by wind and waves. Each coastal region has differing conditions affecting the formation of sea foams. It is a natural phenomenon of the ocean which involves formation of white lathery substance which floats on the surface of water and gets accumulated at the sea shores. The formation of sea foam is seen in several parts of the world and continues to intrigue people even today.

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. According to a 2011 paper* by several Austrian scientists called "Foam in the Aquatic Environment," in order for foam to form, you need air, water, and a key third ingredient called a "surfactant"--a kind of sticky molecule that clings to the surface between water and air. This surfactant ingredient can come from a lot of places; human-made sources include fertilizers, detergents, and sewage. But surfactants also come from the proteins and fats in algae, seaweed, and other marine plant life.

There are lots of different molecules that can act as surfactants, but they all have one thing in common: one end of the molecule is hydrophilic (attracted to water) while the other end is hydrophobic (repelled by water). When a bunch of surfactant molecules get mixed together with plenty of water and air, they all want to line themselves up at the boundary, with one end (hydrophilc) facing the water and the other (hydrophobic) facing the air. They'll even line up, so that the hydrophilic ends are pointed at each other, with a thin layer of water in between. That thin layer of water takes the shape of a sphere, because a sphere requires the least energy of any shape, it's a bubble. Things get slightly more complicated when there are many bubbles packed together--as you might have noticed while taking a bubble bath as a kid (or as an adult), foamy bubbles aren't perfect spheres--but the basic idea is the same. It's all about the surfactant.

Most sea foam is not harmful to humans and is often an indication of a productive ocean ecosystem. But when large harmful algal blooms decay near shore, there are potential for impacts to human health and the environment. Along Gulf of Mexico beaches during blooms of Karenia brevis, for example, popping sea foam bubbles are one way that algal toxins become airborne. The resulting aerosol can irritate the eyes of beach goers and poses a health risk for those with asthma or other respiratory conditions.

*Katerina Schilling and Matthias Zessner. Foam in the aquatic environment. Water Research . Volume 45, Issue 15 , 1 October 2011, Pages 4355-4366