Water-quality profile data were collected in Las Vegas Bay and near Sentinel Island in Lake Mead, Arizona and Nevada, from October 2000 to September 2004. The majority of the profiles were completed with automatic variable-buoyancy systems equipped with multiparameter water-quality sondes. Profile data near Sentinel Island were collected in August 2004 with an automatic variable-depth-winch system also equipped with a multiparameter water-quality sonde. Physical and chemical water properties collected and recorded by the profiling systems, including depth, water temperature, specific conductance, pH, dissolved-oxygen concentration, and turbidity are listed in tables and selected water-quality profile data are shown in graphs.