Downstream and upstream they are landmarks of a river by the sight of an observer. Downstream is the normal flow of water, from a higher point to a lower point. amount is the direction of from lowest point to highest.
Downstream is the side where the water flows and upstream is the part where the river starts. Therefore, it is said that the mouth of a river is the most downstream point of this river, and the source is its most upstream point.
The term downstream comes from the Latin "jusum" which means ebb, towards the mouth, that is, all water that goes down to the mouth of the river is downstream and upstream is the part above, where the waters come from. This reference point can be a city on the riverbank, a dam, a waterfall, a tributary, a bridge, etc.
the adverbial phrase downstream refers to the underside or descending: towards the mouth. It is used to reference a lower point, being at a higher point. It refers to the side that ebbs the tide.
the adverbial phrase upstream it refers to the direction of the spring, it refers to the highest point (spring).
In figurative language, the adverbial phrases “upstream” and “downstream” are used to refer to events before (upstream) or after (downstream) a given date. These terms are used in several areas, especially in the exact sciences.