The priests who bore the ark of the covenant of Yahweh stood firm on dry ground in the midst of the Jordan; and all Israel passed over on dry ground, until all the nation were passed clean over the Jordan.
There is additional information here in  Joshua 3:17.  At some point in the progress of Israel over Jordan, the priests moved into the very midst of Jordan, where they stood until the passage was completed.  "The priests bearing the ark first took up their stand on the brink of the river, but as they advanced to mid-channel, the river was dried up before them."[26]