Wireless Sensor Networks are emerging as an innovative technology that can revolutionize and improve our daily lives. Nevertheless, the use of such a technology raises new chal- lenges regarding the development of reliable and secure sys- tems. Securing WSN is thus imperative and challenging. Un- fortunately, the conventional security measures based on data encryption are not well suitable to WSNs due to energy and computational resource constraints. However, watermarking techniques usually have light requirements of resource. This paper proposes a new fully distributed watermarking ap- proach for WSNs. This approach is focused on ensuring in- tegrity and authenticity of data. Moreover, in our approach watermark payload and computational complexity are low. The proposed approach is implemented and simulated with the CupCarbon simulator. The simulation results show that the proposed method is energy efficient.