Something that is moving ~ is moving towards the mouth of a river, from a point further up the river. Something that is ~ is further towards the mouth of a river than where you are.
We had drifted ~.
? upstream
ADV: ADV after v, be ADV, n ADV, oft ADV of/from n
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Downstream is also an adjective.
Breaking the dam could submerge ~ cities such as Wuhan.
? upstream
ADJ: ADJ n