Thomas C. Winter is a senior research hydrologist with the U.S. Geological Survey in Denver, Colorado. He earned B.A. and M.S. degrees in geology and a Ph.D. in hydrogeology at the University of Minnesota. From 1961 to 1972, he conducted geological and water resource studies in Minnesota and was in charge of USGS groundwater studies there from 1968 to 1972. Since 1973, he has conducted research on the hydrology of lakes and wetlands, with emphasis on their interaction with groundwater and evaporation. In the late 1970s, he helped establish, and has since been a principal investigator at, four