A fish finder is an electronic device used by anglers to locate fish underwater. It works by sending out sound waves, which bounce off objects like fish and the ocean floor. The device then displays this information on a screen, helping users identify the depth and location of fish. Fish finders come in various types, including portable models and those built into boats. Many modern fish finders also feature GPS technology, allowing users to mark fishing spots and navigate to them easily. Popular brands include Humminbird, Lowrance, and Garmin, each offering different features to suit various fishing needs.