A narrow inlet is a body of water that is typically shallow and has a narrow opening to the sea. The term can refer to three different types of bodies of water: a RIA, FJORD, CREEK, or FIRTH. A RIA is a coastal inlet formed by the partial submergence of an unglaciated river valley. A FJORD is a long, narrow, deep inlet of the sea between steep cliffs created by glacial erosion. A CREEK is a small stream or a narrow, coastal inlet. Lastly, a FIRTH is a long, narrow estuary in Scotland.