Abstract: The analysis of the results of numericalhydrodynamic modeling of water level and current fluctuations of theBaltic Sea in the periods of floods in the Finland and Riga gulfs iscarried out. It is shown that due to the considerable isolation of thesea a great influence on the dynamics of flood waves have the processesthey reflect, resulting in a generated progressive-standing waves.During a especially dangerous sea level rise on January 9, 2005, theflood wave had a period of about 40–42 hours. This period turned out tobe close to the 41-hour period of the Baltic Sea, distinguished on thebasis of an analysis of the results of numerical hydrodynamic modelingof free Baltic Sea level oscillations. The spatial structure of thelevel field for eigenoscillations with a period of 41 hours allows themto be identified as multinodal progressive-standing waves, characterizedby a large number of amphidromic systems and antinodes. One of the mostpronounced antinodes of eigenoscillations with a period of 41 hours isin the Neva Bay of the Gulf of Finland.