‘ And Joshua set up twelve stones in the midst of Jordan, in the place where the feet of the priests who bore the Ark of the covenant stood, and they are there to this day.'
As well as setting twelve stones from the river on the land, Joshua also arranged for the placing of twelve stones in the river from the land. This was a wise move. The twelve stones on the land could be vandalised or removed by enemies but those in the river, placed so as to be obvious from the shore, would not be likely to be so treated. They may have been placed by the ford so as to be in shallowish water, which may well have been where the priests crossed and stood. The stones were there as replacing the priests. There may well have been twelve priests bearing the Ark as representing the tribes. But every time an Israelite crossed the ford at that point he would see the stones in the water and remember how the priests had stood in the Jordan riverbed with the Ark of YHWH their God, Lord of the whole earth, and how it had been dry.
“They are there to this day.” This could have been said a few years later. It is not necessarily an indication of a long gap. Could this suggest that the stones placed on the land were not in fact there to that day?
Alternatively we could read the whole verse as meaning (to paraphrase and amplify) ‘and Joshua set up the twelve stones which had been laid down (per Joshua 4:8). These were twelve stones which were previously in the midst of Jordan in the place where the feet of the priests which bore the Ark of the covenant stood (as mentioned in Joshua 4:3), until he arranged for them to be taken up and set in their night's lodging place, and they are there to this day'. So ‘in the midst -- stood' is seen as explaining which stones were in mind and where they came from. NIV reads it this way. But if it is so it reads very awkwardly.