In particular branches of the Earth sciences the term estuary is used with various meanings. The term estuary is applied to objects that often differ from the original geographic meaning of the word. The phenomena that accompany them and processes that cause them are called also estuary phenomena and processes. The aim of the study is to describe, in a geographic context, the range in meaning of both the term and names of phenomena and processes derived from it. In the years 2002 - 2005, a survey of the distribution of chloride concentrations was conducted on five lakes characteristic of the southern Baltic coast: Jamno, Bukowo, Wicko, Kopań and Łebsko. It was observed that seawater intrusions into the coastal lakes only resembles those that occur in classic estuaries, though the results are similar to seawater intrusion processes. In the Polish section of the southern Baltic coast, coastal lakes are not the only places where these phenomena are observed. We suggest that all inland water bodies that are under the influence of marine intrusions should be called coastal waters, instead of the misleading term estuary.
