(i.e., Fresh-water Sea), an extensive lagoon, in the northern part of the Prussian provinces of East and West Prussia. It is 48 miles in length from S.W. to N.E., and from 4 to 10 miles in width. It is separated from the Baltic by a narrow tongue of land 43 miles in length, at the eastern extremity of which it communicates with that sea by a channel called the Gatt.