Robert M. Hirsch (born June 6, 1949) is a research hydrologist and a former Associate Director for Water of the U.S. Geological Survey. As Associate Director (also known as Chief Hydrologist), he was responsible for the water science programs of the USGS. These include water-related research, the collection of data on rivers and ground water, assessments of water quantity and quality. He served as the leader of USGS water science from 1994 to 2008 when Dr. Hirsch transitioned to the USGS National Research Program to rededicate himself to advancing the science on critical issues of climate change and long-term trends in water resources.