Some of the most dramatic coastlines occur when the ocean flows into mountainous river valleys.
One example, Dalmatian coastlines, are named for the coast of Dalmatia, on the Adriatic Sea. There, the water flooded mountain valleys parallel to the coastline, creating inland sounds, or long inlets of water, running in the same direction as the coastline.
Rias, which can be found in southwest England, are flooded valleys that run perpendicular to the coast.
The ocean can also infiltrate low-lying riverbeds. An estuary is a flooded river mouth on a mud plain. At low tides the ocean water recedes to uncover many creeks and little islands of mud.
While fjords are steep water- filled valleys created by glaciers in highlands, fjards are lowland ocean inlets created by glaciers and studded with small islands. Southern Sweden has many fjards.