This record describes Hydrology (HYD) data collected from the Marine National Facility (MNF) RV Investigator voyage IN2021_V03, titled "Integrated Marine Observing System: monitoring of East Australian Current property transports at 27S." The voyage took place between May 8 and June 3, 2021 departing from Hobart (TAS) and arriving in Brisbane (QLD). Nutrient samples were analysed using segmented flow SEAL AA3 and results are in µmol/L. In-house methods SOP 001, SOP 002, SOP 003 and SOP 004 were used to analyse nutrients. Please cite the following paper when using Hydrochemistry data for silicate, phosphate, nitrate+nitrite (NOx) and nitrite analysis: Rees, C., L. Pender, K. Sherrin, C. Schwanger, P. Hughes, S. Tibben, A. Marouchos, and M. Rayner. 2018. Methods for reproducible shipboard SFA nutrient measurement using RMNS and automated data processing. Limnol. Oceanogr: Methods Doi:10.1002/Iom3.10294 Salinities were analysed using Guildline 8400B Autosal Lab Salinometer and OSIL software. The salinometer was calibrated with IAPSO standard seawater P163 and P164. In-house method SOP 006 was used to analyse salinity, units are Practical Salinity Unit (PSU). Dissolved Oxygens were analysed using Scripps UV titrator and software, units measured in ml/L and converted to µmol/L. Dissolved oxygen was analysed using in-house method SOP 005. All data was processed with HyPro 5.7 on the ship and any data re-processed on shore was with HyPro 5.7. A copy of HyPro is available with the data. Nutrient data decimal places within the CSV file; silicate is 1 decimal place, nitrite is 3 decimal places and NOx (nitrate + nitrite), phosphate and ammonium is 2 decimal places. Previously values below detection limit were set to zero these values are now displayed as the measured value even if that is a negative value. Oxygen Data is displayed to 3 decimal places. Salinity data is displayed to 4 decimal places, prior to in2018_t01 voyage it was 3 decimal places in the csv file. Data processing notes are in the process report (in2021_v03_HYD_ProcessingReport.pdf). This dataset has been archived at the CSIRO National Collections and Marine Infrastructure (NCMI) Information and Data Centre (IDC) in Hobart. Additional information regarding this dataset is contained in the Voyage Report and Data Processing Report.