Digital Hydrographic Maps were developed by means of a geographic information system in order to predict how nesting islands for the American White Pelican (Pelecanus erythrorhynchos) are likely to become land-bridged under variable water levels on Clear Lake Reservoir, California. As a management tool, the maps can be matched to water surface elevation changes forecasted by the U.S. Bureau of Reclamation every year. This graphic method has allowed Klamath Basin National Wildlife Refuge managers to set up electrified fences at Clear Lake Reservoir in advance of the nesting season, successfully protecting nesting colonies on two recent occasions. Digital Hydrographic Maps were also used to match historic hydrographic records for Clear Lake Reservoir to examine past lake conditions and changes in nesting island locations, particularly when nesting failures had occurred. Modifications to existing nesting islands are suggested, so as to create more stable nesting habitat.