The U.S. Geological Survey (USGS) Coral Reef Ecosystems Studies (CREST) project (https://coastal.er.usgs.gov/crest/) provides science that helps resource managers tasked with the stewardship of coral reef resources. Coral reef organisms are very sensitive to high and low water-temperature extremes. Therefore, it is critical to precisely know water temperatures experienced by corals and associated plants and animals that live in the dynamic nearshore environment to document thresholds in temperature tolerance. This data release provides underwater temperature data recorded every fifteen minutes from 2009 to 2024 at ten offshore coral reefs in the Florida Keys, USA. From southwest to northeast, these sites are in Dry Tortugas National Park: Garden Key, Pulaski Shoal West, Pulaski Shoal Light; in the Florida Keys National Marine Sanctuary: Sombrero Reef, Crocker Reef, Molasses Reef; and in Biscayne National Park: Ball Buoy North, Shadow Reef, Brewster Reef, and Fowey Rocks. Measurements were made at Sombrero Reef from July 2009 to August 2022, at Crocker Reef from June 2013 to August 2022, and at Molasses Reef from April 2009 to April 2013. Data collection continues at three sites in the Dry Tortugas National Park (Pulaski West, initiated December 2016, Garden Key, initiated May 2022, and Pulaski Light, initiated June 2009) and four sites in Biscayne National Park (Fowey Rocks, initiated August 2009, and Ball Buoy North, Shadow Reef, and Brewster Reef initiated in May 2023). The data release will continue to be updated, as more data are collected. Portions of the dataset included here were interpreted in conjunction with coral and/or algal calcification rates in publications including Kuffner and others (2020) and Lenz and others (2021). See the cross-reference section of the metadata for a complete list of related publications.