A whitecap is a wave on the ocean or a large lake that has broken at its crest, creating white foam at the top. The name comes from what you see: the breaking wave looks like it's wearing a white cap or hat made of bubbles and spray.

Whitecaps form when wind blows hard enough across water to make waves steep and unstable. As a wave grows taller, its top moves faster than its bottom, and eventually the crest topples over, creating that characteristic white, foamy appearance. Sailors and weather watchers use whitecaps as clues about wind conditions. When you see whitecaps appearing on a lake or bay, you know the wind is blowing at least 12 to 15 miles per hour. The more whitecaps you see, and the bigger they are, the stronger the wind.

On a breezy day at the beach, you might notice just a few whitecaps scattered across the water. During a storm, the entire surface of the ocean can become covered with whitecaps, creating what sailors call a white sea. The foam itself comes from air mixing with water and organic materials from tiny sea creatures, which can act like soap and help create stable bubbles that last for several minutes before dissolving back into the waves.