Delta and Estuary

A River Delta is a landform that forms at the mouth of a river, where the river flows into an ocean, sea, estuary, lake, or reservoir. 

Deltas form from deposition of sediment carried by a river as the flow leaves its mouth. 

Over long periods, this deposition builds the characteristic geographic pattern of a river delta.

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An Estuary is a partly enclosed coastal body of brackish water* with one or more rivers or streams flowing into it, and with a free connection to the open sea. 

Estuaries form a transition zone between river environments and maritime environments and are subject to both marine influences, such as tides, waves, and the influx of saline water; and riverine influences, such as flows of fresh water and sediment. 

The inflows of both sea water and fresh water provide high levels of nutrients in both the water column and sediment, making estuaries among the most productive natural habitats in the world.

*Brackish water or briny water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers