"The road ran parallel to a fast-moving stream, running eastward from Topal Bay. It was called the Onkobra River."
Waughin Jarth[src]

The Onkobra River was a river in the Imperial province of Black Marsh, or Argonia as it was known to the native Argonians.[1] It flowed from Topal Bay inland into the swampy heart of Black Marsh,[1] and was said to possess a strong current.[2] It was located near the Argonian city of Gideon.[1]

During the Third Era, an Imperial road ran parallel to the river.[1] The Onkobra was also bordered by the estates and plantations of the Archeins,[1] native Argonians who governed the rural areas of Black Marsh,[3] as well as farms,[1] orchards,[1] and vineyards.[1]