What is the definition of a main river channel?
(at less try) to put it in your own words.
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I can't/don't know how to make it in me own words but here's the definition

In physical geography, a channel is a type of landform consisting of the outline of a path of relatively shallow and narrow body of fluid, most commonly the confine of a river, river delta or strait. The word is cognate to canal, and sometimes shows in this form, e.g. the Hood Canal. Most examples of this are fjords in the Pacific Northwest; a notable exception is the Casiquiare canal. All likely share borrowing from Spanish, Portuguese or French.