Introduction: The objective of this study was to identify primary health care nurses' competencies when responding to hydrological disasters in rural areas. Methods: A descriptive, exploratory and qualitative study was developed. The Critical Incidents Technique was adopted. Twenty public health nurses who worked during the flood season in the years 2014 and 2015 in a rural area in southern Brazil were interviewed. Critical incidents and requirements identified in the data gave rise to the development of the competencies. Results: Thirty competencies were identified and classified in the domains of leadership and management, teamwork, health care, being community-oriented, communication, psychological support, health surveillance and education. Conclusions: Although the competencies could be related to the established international competencies for nurses in disasters, a number were described only in this study. These competencies can contribute to the education and practice of nurses in primary health care, strengthening the capacity of the profession to face flood disaster situations in rural areas.