Fresh water and energy supplies are two main themes for global sustainable development. As the largest resource storehouse, the ocean has massive seawater and inexhaustible tidal energy. Exploration and utilization of ocean resources have become an inevitable trend; however, current ocean-exploring equipment mostly works with postures of floating, suspending, and deep diving. Considering important demands of signal transmission, energy acquisition, and working secrecy, developing intelligent devices that can dive just underneath water surfaces requires significant concerns. Learning from elegant postures of aquatic insect backswimmer, here, we demonstrate an intelligent underwater device with controlled diving postures and depths regardless of different water environments. Further, potential applications of the device are exhibited in terms of solar steam generation, water-wave sensing, and wave-energy collection. These findings can improve the understanding of natural interface phenomena and offer protocols to design autonomous interface locators, diving miniature robots, and more smart devices for ocean-resource exploitation.