Aplace where salt water and fresh water meet is called a(n) .tributary or an estuary

An estuary is where salt water and fresh water meet. Estuaries are usually found at the edge of the coast, where the ocean water, or salty water, meets river, lake, any fresh water source, water.

A tributary is something completely different. It is a, usually smaller than the main river or lake, river/stream stemming off a bigger river or lake, or flowing into that river or lake.