Firth

A firth is a coastal geographical feature that refers to a broad inlet or estuary where a river meets the sea. In common usage, firths are tidal, shallow, and wide, with a mix of freshwater and seawater and often surrounded by marshes, mudflats, or islands. The term is especially associated with Scotland, where many major inlets are called firths, though it can describe similar tidal valleys in other regions.

Firths are typically formed when rising sea levels flood river valleys, creating broad, gently sloping estuaries that are strongly influenced by tides. They are generally distinct from fjords, which are deep, narrow, and formed primarily by glacial carving, whereas firths tend to be wider and more tidal. The landscape around a firth often includes salt marshes, estuarine habitats, and diverse birdlife, making them important for ecosystems and, in many places, for human activity such as fishing, shipping, and port development.

Notable examples in Scotland include the Firth of Forth near Edinburgh, the Firth of Tay near Dundee, the Firth of Clyde along Scotland’s west coast, and the Firth of Lorne on the western seaboard. While the term is most common in Scotland, it is used in naming inlets and estuaries in other parts of the British Isles and beyond.

Firth also appears as a surname. Notable bearers include the English actor Colin Firth. As a place name and surname, the word retains cultural and geographic associations with coastal landscapes and maritime history.