River mouth

The water from a river can enter the receiving body in a variety of different ways. The motion of a river is influenced by the relative density of the river compared to the receiving water, the rotation of the Earth, and any ambient motion in the receiving water, such as tides or seiches.

If the river water has a higher density than the surface of the receiving water, the river water will plunge below the surface. The river water will then either form an underflow or an interflow within the lake. However, if the river water is lighter than the receiving water, as is typically the case when fresh river water flows into the sea, the river water will float along the surface of the receiving water as an overflow.

Alongside these advective transports, inflowing water will also diffuse.

Landforms

At the mouth of a river, the change in flow conditions can cause the river to drop any sediment it is carrying. This sediment deposition can generate a variety of landforms, such as deltas, sand bars, spits, and tie channels. Landforms at the river mouth drastically alter the geomorphology and ecosystem. Along coasts, sand bars and similar landforms act as barriers, sheltering sensitive ecosystems that are enriched by nutrients deposited from the river. However, the damming of rivers can starve the river of sand and nutrients, creating a deficit at the river's mouth.