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. 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 dataset provides underwater temperature data recorded every fifteen minutes from 2009 to 2022 at seven off-shore coral reefs in the Florida Keys, USA. From southwest to northeast, these sites are Garden Key (Dry Tortugas National Park), Pulaski Shoal West (Dry Tortugas National Park), Pulaski Shoal Light (Dry Tortugas National Park), Sombrero Reef (Florida Keys National Marine Sanctuary, FKNMS), Crocker Reef (FKNMS), Molasses Reef (FKNMS), and Fowey Rocks (Biscayne National Park). 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 one site in Biscayne National Park (Fowey Rocks, initiated August 2009). The data release will continue to be updated, as needed. 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 publications.