Seismic imaging issues in environments with steep flanks are known to be partly due to the existence of prism waves (also referred to as either prismatic or duplex waves in literature). Prism waves are mainly caused by scattering at steeply dipping structures, such as salt flanks and vertical or nearly vertical faults, and in contrast to turning waves, they are often recorded even when data acquisition aperture is limited. More precisely, prism waves are doubly-scattered waves that reflect from two near-orthogonal interfaces before reaching the receiver located on the surface. Since they contain a lot of information concerning the steep parts of the reflectors, they are very complementary to primary reflections for imaging complex environments. As a consequence, since two decades, there is a wealth of literature dedicated to the modern development of seismic imaging techniques that make the most of the valuable information carried by prism waves, most often in the context of salt body environments. In the literature, prism waves are usually referred to as waves that are doubly scattered in the downgoing direction only. Few works are concerned with prism waves that consist of double horizontal reflections from the steep flanks of reflectors. In this presentation, we investigate the wave reflections from a seafloor of canyon type. They may be of three types : (i) the primary reflection that is always present and that may go through a caustic, depending on the curvature of the canyon ; (ii) two side reflections, depending on the curvature of the sides of the canyon ; (iii) prism waves of different kinds (namely, singly-reflected and doubly-reflected canyon waves). We discuss analytically the conditions of existence of all these waves and illustrate numerically their propagation for different curvatures of the canyon.