Short answers, pulled from the story.
Scholars interpret the word Oium as a dative plural noun from Germanic languages with a Proto-Germanic reconstruction of awjō meaning well-watered meadow or island. The noun derives from ahwō which means water, stream, or river and is cognate with Latin aqua meaning water.
Jordanes himself understood Oium to be near Sea of Azov which was considered a marshy area during his period. Herwig Wolfram proposes that an uncrossable river might be Dnieper based on this proposal while Norbert Wagner suggests marshes surrounding Oium could be Pripyat or Rokitno marshes west of Dnieper near modern border of Belarus and Ukraine.
In the year 551 a scribe named Jordanes wrote a text called the Getica which became the primary source for the legend of Oium. He claimed the land was fertile and rich but admitted he preferred written sources over old wives tales.
It is said when half army had been brought over bridge fell into utter ruin making it inaccessible thereafter. Place is surrounded by quaking bogs and encircling abyss so no one could pass to or fro after that event.
Archaeologically Chernyakhov culture also called Sântana de Mureș contained parts of Ukraine Moldova and Romania corresponding with extent of Gothic-influenced Scythia known from third and fourth century contemporaries. For archaeologists subscribing to Vistula migration proposal Wielbark culture represents earlier Goths while Jordanes account fits interpretation of both Wielbark and Chernyakhov cultures.