We present a general framework for building mobility models for floating objects. Such models are useful for studying the behavior of wireless sensors that are deployed to drift along rivers, lakes, oceans, or debris flows. These sensors may be used to track toxic wastes in the water, to study hydrology, or to warn natural hazards. While existing mobility models concentrate on modeling objects moving in autonomy on firm grounds, they cannot be used to describe floating objects that move along with the water flows passively. To build mobility models for such floating objects, our framework entails the use of GPS-equipped wireless sensors that drift along with the water and record the path information. The collected information is converted into a two-dimensional map for modeling the behavior of the floating objects, e.g. generating the simulated drifting paths of the objects. As far as we know, this is the first work on building the mobility models for floating objects.