tributary or estuary
Two rivers that join the Mississippi River are the Missouri River and the Ohio River.
Allegheny, Monongahela, and Ohio Rivers
Confluence-a point at which two or more rivers become one. Confluence- a point where tow or more rivers/streams become one.
The rivers Yonne, Marne, and Oise are the main rivers joining the Seine river along its course.
The confluence of the Alleghaney and Monogahela Rivers form the Ohio River at Point State Park in Pittsburgh. Thus the three rivers that "come together" at that point are the Ohio, Allegahaney and Monogahela.
mississippi/missouri
tributries
A place where two rivers join.
Tributaries are the smaller rivers and where they join is called a confluence
Tributaries. Or maybe braided rivers, I can't remember.
A junction. I live in a place called Grand Junction where three rivers merge.
American and Feather