A river always has
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Delta
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Tributaries
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Boats
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Banks
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Fishes
A river must have banks (sides) to contain and define its channel. Without banks, water would simply spread out rather than form a flowing river. Tributaries, boats, and fishes are commonly associated with rivers but are not essential - a river can exist without them. Delta is a landform formed at some river mouths, not present in all rivers.
A river is defined as a natural flowing channel of water, and by definition it must have banks — the land on either side that contains its flow. Not every river has a delta (some end in estuaries or simply dry up), not every river has tributaries or fish, and boats are man-made additions, not an inherent feature. Banks are the one structural feature every river must have to be a river at all.