A multi-use, multi-level structure can be installed in and removed from a body of water in a seasonal fashion. The structure has a lower level that includes a boat lift and an upper level that provides an entertainment area. The structure carries a buoyancy system for selectively floating the structure on the body of water or sinking the structure in the water. The buoyancy system preferably comprises a ballast system that includes an array of hydraulically interconnected ballast tanks that are vented to the atmosphere. A valve may be opened to admit water to the ballast tanks to flood the tanks. A pump is used to pump water out of the ballast tanks when desired.