A medium-sized inflow (about 200 km³ according to IOW data, - personal communication) of saline water into the southern Baltic Sea occurred during January 2003. Unlike any previously observed inflow, this one brought very cold water, of temperatures around 1-2^oC and less. Since the temperature of the deep water in the southern Baltic before the inflow was exceptionally high (11-12^oC), the inflowing waters produced dramatic changes and a steep temperature gradient. The movement of the inflowing waters through the deep basins and channels of the Baltic Sea from the Arkona Basin to the Gdańsk Deep during next 4-8 months is described. Frequent mesoscale structures and intensive mixing followed the eastward transport of the inflow water, particularly in the Bornholm Deep and Słupsk Furrow. The present paper is based on data collected during 6 cruises r/v "Oceania" between December 2002 and August 2003. The last cruise in August took place in order to assess the long-term consequences of the inflow.