This report summarizes the hydrologic setting and the water-resources investigations in the Southwest Florida Water management District performed by the U.S. Geological Survey, Water Resources Division, for fiscal year 1979. Hydrologic conditions in southwest Florida are described and illustrated by hydrographs of selected surface-water, ground-water, and lake-stage data-collection sites. In addition, summaries of water-use data and data on the regional observation monitor-well program are provided. The investigations are pay of the Federal program of appraising the nation's water resources.l The cooperative program for fiscal year 1979 included 37 investigations. Abstracts of 15 reports released during 1979 are included.