A depth finder is a device used to measure the distance from the water's surface to the bottom of a body of water. It is commonly used in boats and fishing to help navigate and locate underwater features. Depth finders use sonar technology, sending sound waves down and measuring how long it takes for the waves to bounce back. These devices can display depth readings in real-time, allowing users to avoid shallow areas and find optimal fishing spots. Many depth finders also come with additional features, such as GPS integration and fish finders, which help anglers locate fish more effectively.