Аннотация:The article contains the description of the geological structure and relief of Penzhina river estuary, as well as the adjacent part of Penzhina Bay, examined during the field work in August of 2014. The main pre-Quaternary rock complexes of Mesozoic-Cenozoic are analyzed. Main attention is given to the structure of the coasts; the main geomorphological levels were distinguished. For the first time the composition of sediments and the relief of the tidal dewaterings, the distribution and types of modern geomorphic processes were studied in detail. The reason of high water turbidity which is characteristic for the Penzhina mouth area during tidal fluctuations were clarified – it is the erosion of dense clay presumably of lake origin lying at the base of the low terraces. The signs of intense coastal erosion during high tides and surges were identified.