Opportunistic wireless transmission is a technique offering collaboration of simultaneous flows to achieve error resilient transmissions. In this paper, we introduce the use of opportunistic wireless transmission for data diffusion which deals with the all-to-all data dissemination in a wireless sensor network. Our design turns the network infrastructure into a single fountain encoder where source packets arrive from each sensor node and these packets are encoded while flooding throughout the entire network to all nodes. Simulation and analysis are carried out showing that our proposed opportunistic data diffusion achieves efficient and error resilient all-to-all data dissemination. The results confirm that our solution offers not only efficient and reliable all-to-all data dissemination over lossy wireless links, but also scalability to large networks.