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 ballast system for selectively floating the structure on the body of water or sinking the structure in the water. The ballast system 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.