The difference between an estuary and delta :

Estuary

• When there are no distributaries of a river and it meets an ocean or a sea in a single line, then the lower course of the river is called an estuary.
• An estuary is formed in coastal areas of high tides an rift valleys.
• The coastal areas near estuaries are suitable for natural harbours.

Delta

• When a river meets an ocean or a sea with so many distributaries, they are forming a triangular shape due to silt deposits, is called a delta.
• A delta is formed in coastal areas having plains and visiting by low tides.
• Coastal areas having delta formations are good for agriculture and have artificial harbours.