This U.S. Geological Survey (USGS) Data Release provides water-quality data collected during 1-week and 2-week nutrient studies beginning on February 22, May 17, and July 26 located in the Caloosahatchee River at the S-79 water-control structure. For each study period, 12 fiberglass tanks were suspended in the river using three floating cradles with each cradle holding four tanks. Each tank was open to the atmosphere and closed to the river. The tanks were filled with native water during the first day of each study period. Four different treatment methods were represented within each cradle. For all three study periods, two of the four treatments remained constant: ammonium hydroxide and untreated. For the 1-week study period in February, the additional treatment methods were sodium phosphate dibasic dodecahydrate and sodium nitrate. For the 2-week study period in May, the additional treatment methods were sodium phosphate dibasic dodecahydrate and urea. For the 2-week study period during July-August, the additional treatment methods were sodium nitrate and urea. Treatments were added to the tanks following the profiles on the first day of each study period. Nutrient samples were collected and processed by Nova Southeastern University. Water-quality sensor data were collected near the surface (approximately 1 foot below the water surface), near the middle of the water column (approximately 2 feet below the water surface), and near the bottom (approximately 3 feet below the water surface) of each tank using a multi-parameter water-quality sonde. Additional water-quality sensor data were collected at approximately 1, 2, and 3 feet below the water surface within the river. Each point reading is provided as an instantaneous measurement. Water-quality parameters measured include water temperature, specific conductance, pH, dissolved oxygen, turbidity, phycocyanin fluorescence, chlorophyll fluorescence, and fluorescence of dissolved organic matter. Revision History: First release: November 2023. Version 1.1: August 2024. Changes from previous version: in file "Mesocosms_profiles_2021_datarelease_data" revised one of the four treatment methods for the July-August study period from sodium phosphate dibasic dodecahydrate to sodium nitrate to correct an Excel entry error.