Metamaterials, initially developed for electromagnetic and acoustic wave manipulation, have recently emerged as a powerful tool for controlling water waves. These engineered structures exhibit unique properties not found in natural materials, enabling unprecedented control over wave propagation, refraction, and focusing. This review offers a comprehensive overview of metamaterials for water wave applications, emphasizing their theoretical foundations, design methodologies, and practical implementations. It begins by outlining the fundamental physics of water waves and the key equations governing wave phenomena. Then, the principles and design of metastructures, which serve as the fundamental building blocks of water wave metamaterials, are explored. This focus includes various metadevices, such as invisibility cloaks, wave concentrators, rotators, and superscatterers. Through an extensive analysis of both numerical and experimental studies, this paper provides a roadmap for future research and technological advancements in water wave metamaterials, highlighting their potential to address challenges, particularly in ocean energy harvesting, coastal defense, and disaster prevention.