A River Never Becomes a Firth—They're Different Landforms

A river does not become a firth. They are distinct:

• River: Natural freshwater channel flowing downhill from source to mouth (sea, lake, another river).
• Firth: Scottish term for a coastal inlet—sea loch, estuary, bay, or strait—where seawater penetrates land. Salt/brackish water.

Relationship

A river flows into a firth (e.g., River Forth → Firth of Forth; River Clyde → Firth of Clyde). The firth is the marine receiving basin, not the river's transformation.