Aquatic interfacial materials that regulate multiphase interactions are pivotal for environmental and energetic applications, yet traditional rigid floaters lack morphological adaptability and integrated flexibility. Inspired by the active buoyancy regulation of Microcystis, we present a floatable and integrated shape-shifting (FISS) hydrogel, combining solid-like robustness with liquid-like adaptability for advanced floating carriers. The in situ formation of amorphous magnesium carbonate (AMC) nanoparticles provides dynamic crosslinking points for the FISS hydrogel, and the incorporation of amino-functionalized hollow microspheres serves a dual role as tunable buoyancy units and secondary crosslinking hubs. This microstructural engineering establishes a thermodynamically stable state of "limited fluidity," allowing the hydrogel to adopt a hydrostatic equilibrium on water surfaces while preventing uncontrolled dissipation. Based on its flexibility and deformability, FISS hydrogel exhibits versatile interfacial functions, including evaporation suppression, pollution shielding, biomimetic underwater gas capture, etc. Through the assembly by interfacial adhesion of FISS hydrogel, the carrier diversity is further demonstrated as an attitude-tunable evaporator and a light-driven flexible detector. This work presents a design strategy for a hydrogel-based floater exhibiting flexibility and integrability, which can extend the application scenarios of hydrogel materials.