This portion of the USGS data release presents acoustic-backscatter data collected during surveys performed in Floras Lake, Oregon in June 2018 (USGS Field Activity Number 2018-636-FA). Lake bed backscatter data were collected using a personal watercraft (PWC) equipped with a sidescan sonar system and global navigation satellite system (GNSS) receivers. The sonar system consisted of a Tritech Starfish 990F with a 1-MHz transducer and a 0.3-degree horizontal beam width. Output from the GNSS receivers and sonar system were combined in real time on the PWC by a computer running HYPACK hydrographic survey software. Navigation information was displayed on a video monitor, allowing PWC operators to navigate along survey lines at speeds of 2 to 3 m/s. Survey-grade positions of the PWCs were achieved with a single-base station and differential post-processing. Positioning data from the GNSS receivers were post-processed using Waypoint Grafnav to apply differential corrections from a GNSS base station with known horizontal and vertical coordinates relative to the North American Datum of 1983.