meaning of "that takes most of the water down it"

[Learning_English]

main current -- A river has a main current that takes most of the water down it, with subsidiary currents where the flow is interrupted.

Please explain (that takes most of the water down it)
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Please let me know if I have made any mistakes in any of my sentences.

[Yankee]

Hi Learning_english

The word 'that' refers to 'main current' and the word 'it' refers to 'river'.
The main current is what causes most of the water in a river to move down the river.

Does that clarify things for you?

Amy

[Learning_English]

[Conchita]