The work discusses the peculiarities of the water spread on the mouth of the Keret river (Kandalaksha Bay, White Sea). Tidal phenomena are pronounced in the mouth of the rivers of White Sea basin. The study of hydrological regime of Keret estuary has been regularly carried out in recent years by the Departments of Hydrology, Oceanology and Earth Physics of St. Petersburg State University. The Keret river's streamflow is not regulated. The river is characterized by a small flow of sediments, and the average annual river discharge is 22.6 m3/s. The range of river water distribution is affected not only by the intensity of marine processes, but also by the changing volumes of Keret waters entering in the White Sea at the end of the spring flood.