This dataset is a polygon shapefile containing reservoir boundary of Lago Guayabal, and represents the contour at the spillway elevation. This polygon was used to constraint the extent of the Triangulated irregular network (TIN) model and ultimately, to generate contours from bathymetric data collected during a sedimentation survey conducted during the period December 11- December 14, 2017 by the Puerto Rico office of the Caribbean-Florida Water Science Center of the U.S. Geological Survey (USGS). The goals of the survey were to determine reservoir infill sedimentation rates, generate a bathymetric map of the reservoir, and create a stage-volume relation. Field techniques used during the survey were similar to those outlined by Soler-López (2008) and Wilson and Richards (2006). More than 270,000 water-depth points were surveyed along 60 navigation lines used in previous sedimentation surveys (Soler-López, 2003, 2008). All water-depth data were collected using a Teledyne-Odom Echotrac CVM depth sounder coupled to a Global Positioning System (GPS). Esri ArcGIS, version 10.5 (reference similar to that in metadata for point shapefile), was used to edit the depth data and create a triangulated irregular network (TIN) model, from which bathymetric contours and a stage-volume relation were generated . References: Soler-López, L.R., 2003, Sedimentation History of Lago Guayabal, Puerto Rico, 1913-2001: U.S. Geological Survey Water-Resources Investigations Report 03-4198, 28 p, 2 pls. Soler-López, L.R., 2008, Comparison of Storage Capacity and Sedimentation Trends of Lago Guayabal, Puerto Rico, December 2001 and October 2006: U.S. Geological Survey Scientific Investigation Map 2008-3016, 1 sheet Wilson, G.L., and Richards, J.M., 2006, Procedural Documentation and Accuracy Assessment of Bathymetric Map and Area/Capacity Tables for Small Reservoirs, U.S. Geological Survey-Scientific Investigation Report 2006-5208, 24 p. plus oversize figs,https://pubs.usgs.gov/sir/2006/5208/pdf/SIR-06-5208.pdf.