Three oceanographic cruises on board of R/V Atlântico Sul were conducted over two years on the Southern Brazilian Continental Shelf (SBCS): in 2023, Albardão I (2023-11-05 – 2023-11-10) and INCT-MarCOI Plataforma/Oceano (2023-11-20 – 2023-11-27) (stations C00 to C05); and in 2024, Albardão II (2024-05-29 -2024-06-04) (stations C06 to C09 for the cross-shelf transect, P06 to P10 for the Patos Lagoon estuarine plume, and A01 to A07 for the along-shelf transect). The study area comprised the southernmost sector of the SBCS, between the estuary of the Patos Lagoon (32°S, 51°W) and Chuí (33°S, 52°W). These cruises aimed to characterize the oceanographic conditions of the region and assess the impacts of the extreme flood event that occurred in southern Brazil in May 2024. Seawater samples and hydrographic data were collected using a CTD-rosette system equipped with a Sea-Bird SBE19plus CTD profiler. During the Albardão I and Albardão II cruises, an additional CTD sensor from JFE Advantech was also used. Water samples were collected using six 4-litre Niskin bottles attached to the rosette system. All onboard sample processing was carried out in a clean laboratory (Clean Lab) housed in a refurbished container, which adheres to the GEOTRACES protocol for trace element sampling (Cutter et al., 2017). On this dataset, stations without inorganic nutrient or 223-Ra samples were named as CTD-data. Water samples for dissolved inorganic nutrient analyses were processed in the Clean Lab, filtered through 0.45 µm cellulose acetate filters (Whatman®), and stored at −17 °C until analysis. Nutrient concentrations were determined following the methods described by Grasshoff et al. (1999) and Strickland and Parsons (1972). The 223-Ra samples were collected using an in situ pumping system at a depth of 1.5 m during the 2024 cruise and at 3 m during the 2023 cruises. Seawater was stored in plastic barrels, with volumes of 200 L for stations located within 100 km from the coast and 400 L for offshore stations. The samples were subsequently passed through Mn-fiber columns for radium extraction and later analyzed using a RADeCC (Radium Delayed Coincidence Counter) system, following Moore and Arnold (1996) and Moore and Cai (2013). All sample analyses were carried out at the Federal University of Rio Grande (FURG). Additionally, five samples of the Patos Lagoon estuarine plume, obtained during monitoring activities conducted by Portos RS in 2011 (stations P01 to P05), were incorporated into the dataset to represent pre-flood conditions. Portos RS provided these data.