Abstract Comprising 17,000 blocks of coal fly-ash, Betty Beaumont’s Ocean Landmark (1978–1980) is an artificial reef located off the coast of Fire Island, New York. This essay analyses the visual inaccessibility of the work and its reliance on an assemblage of media to highlight its significance for conceiving political, ecological and cultural meanings of the ocean. Land art’s fascination with the limits of visuality, the site/non-site dialectic and relationship with industry will provide a framework for this aim. Ocean Landmark’s situatedness and association with industrial ecology signals the wider juridical and political lack of transparency in industrial activity in the ocean spaces framed as sites of unseen environmental extraction. Demonstrating the political and epistemological consequences of a lack of visibility, it challenges the assumptions of total sensorial and epistemic access, highlighting the limitations of anthropocentric positions in and beyond the ocean.