The place where a river branch out into a triangle shape is known as a delta.
A strip of land next to a river that is sometimes covered in water is a flood plain.
It should be noted that a delta refers to an area of low, flat land that has the shape of a triangle where the river will split and then spread out into different branches before it enters the sea.
A flood plain refers to the strip of land that is next to a river that gets covered in water when the river floods.
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