The paper describes the activities led to assess the feasibility and effectiveness of a UAV able to operate in air and water. The situation awareness after environmental calamity usually requires to gather data about the pollution both in air and in water (sea, lakes, rivers) in times as short as possible. An Unmanned vehicle able to collect samples in flight and below the water could provide an effective data retrieval platform, which can be also expendable in case of contamination of the vehicle itself. After a description of the conceptual design phase and sizing/weight breakdown, the paper focuses the attention on the simulation of the UAV both in air and in submerged modality, introducing the dynamics models used in this conceptual phase. The simulation of a realistic mission has been finally implemented to better assess the efficiency and effectiveness of such a vehicle. A final comment section provides notes on the strength and potentialities of such a configuration together with a list of the critical issues which can be encountered during the design/manufacturing of such a kind of robotic vehicles.