We report results of a hydrographic cruise organized within the framework of the Russian-Brazilian joint project SAFARI (Southwestern Atlantic Freshwater Assimilation and River Inputs) and aimed at mapping special features of salinity and temperature distributions connected with the freshwater discharges from the Plata river and Patos-Mirim lagoon estuaries on the Southern Brazilian shelf. Apart from the low salinity tongue in the inner shelf that has not been mapped in detail before, the intense river runoff results in strong temperature inversions (up to 4¿C per 20--30 m) seen in the upper layer in winter. We argue that these inversions cannot result from the advective mechanism alone and should also be attributed to the freshwater related increase of vertical stability that leads to reduced mixing and thus enhanced winter cooling of the sea surface. Spatial distributions of salinity, inversion layer thickness and inversion magnitude over the shelf and continental slope are presented. In a belt extending for hundreds kilometers northward from the Plata estuary in the inner part of the shelf, salinity is up to 10 psu lower than that in the adjacent ocean beyond the river plumes. The spatial extent of the Patos-Mirim lagoon plume is determined and the fine structure of the salinity distribution near the lagoon mouth is described.