This article offers a critical reappraisal of the Maoist state's response to the 1954 Yangzi floods. It uses a variety of sources, including previously classified government reports and oral history testimony, to challenge the official narrative. It argues that, far from being a remarkable victory for the new government, the flood was a humanitarian catastrophe that caused almost 150,000 deaths. Government hydraulic policies were partly to blame, as the vast majority of disaster victims were located in rural areas that were flooded deliberately in order to protect cities. In addition to revealing the true scale of the flood, this article uses the disaster as a prism to examine the early Maoist state. The government's combative environmental policies turned disaster governance into a war on water. This approach had certain benefits, particularly in terms of organizing an effective urban relief campaign. Unfortunately, campaign politics fostered an atmosphere of distrust, which encouraged many citizens to resist disaster-prevention policies. The example of the 1954 flood reveals the profound impact that a political context can have upon the outcome of a supposedly natural disaster.