In cooperation with the Bureau of Reclamation (Lower Colorado Region), the U.S. Geological Survey collected meteorological data from 4/22/2013 to 4/25/2017 at Lake Mead and 4/11/2013 to 9/30/2016 at Lake Mohave. Meteorological monitoring equipment were mounted to a floating platform located at each lake. The data presented in this data release includes 30-minute mean air temperature, relative humidity, wind speed and direction, water surface temperature, net radiation, and incoming solar radiation. Quality assurance consisted of (1) monthly site visits to inspect and clean sensors, (2) recalibrating each sensor as necessary according to manufacturer guidelines, and (3) manual and graphical analysis for out-of-range values and anomalous patterns. Net radiation data were corrected for sensitivity to wind speed (Campbell Scientific, Inc, 2016) and calibrated following the procedures outlined in Moreo and Swancar (2013, p. 7-10). Meteorological data were collected in support of ongoing evaporation research at both lakes.