Early modern Tokyo was a city of water with rivers and canals crisscrossing the city and connecting its commercial centers. However, modern Tokyo's rivers have disappeared-filled in, or converted into concrete-lined sewers. This article explores what happened to these waterways during Japan's period of rapid economic growth. It focuses on the 1961 policy decision by city planners and water engineers that resulted in the rivers-to-sewers transition in the lead-up to the 1964 Tokyo Olympics. The process of making this policy sheds light on the interface of the long-term urban industrial pollution and the short-term pressures of urban clean up before the 1964 Olympics. Contributing an envirotech perspective on industrial waste management during Japan's high-speed economic growth period, this article brings to focus a rush to pave with concrete Japan's return on the international scene, as part of the showcasing recovery from the political and economic catastrophe of World War II.