A breakwater is a strong wall or barrier built out into the ocean or a large lake to protect a harbor, beach, or coastline from the force of waves. Picture a long stone wall extending from the shore into the water, taking the brunt of crashing waves so that boats in the harbor behind it can rest peacefully and people can swim safely at the beach.

Breakwaters work by breaking up large waves before they reach shore, which is exactly how they got their name. When ocean waves slam into a breakwater, their energy scatters and weakens, leaving much calmer water on the protected side. Some breakwaters sit right at the surface like massive walls, while others hide just below the waterline.

Engineers build breakwaters from huge rocks, concrete blocks, or other heavy materials that can withstand constant pounding from waves and storms. Without breakwaters, many harbors would be too rough for boats to load cargo or for passengers to board ships safely. Some coastal towns also use breakwaters to prevent beaches from washing away during storms. Next time you visit a harbor, look for these protective barriers standing guard against the sea.