This paper proposes a technique for the 3D reconstruction of an underwater environment from multiple range views. The final target of the work lies in improving the understanding of a human operator guiding an underwater remotely operated vehicle (ROV) equipped with an acoustic camera, which provides a sequence of 3D images in real time. Since the field of view is narrow we devise a technique for the reconstruction of relevant information of the image sequence up to building a mosaic of the surrounding scene. Due to the very noisy nature of the data and the low range resolution, smoothing, segmentation, registration, and fusion problems have been tackled. Examples on real images are presented to show the promising performances of the algorithm.