[JudgePenitent]

> but the river is gone too.

The Sumerians were well known to forcibly reposition the local rivers of which there were many in the flood plain. There are probably plenty of areas with long lost boats, areas today that wouldn't appear to having been a river, ever.

There's a whole back story here of the Persian gulf which receded something like 100 miles around the time Sumer disappeared[0]. My theory for this is that population growth in the south created caused an expansion of irrigation/agriculture- and as kings became more willing and able to reposition rivers, they unintentionally created the first major human environmental catastrophe. This is why the Akkadians, to the north of the Mesopotamian flood plain, were the inheritors of Sumerian culture. Cities like Uruk would have much been closer to the coast than they are today, giving southern Sumer (in its heyday) a very similar environment to the Nile river delta pouring into the Mediterranean, with all those cities parked right in the middle of the delta.

We know too that southern Sumer was trading heavily with many neighbors, including India, so we can easily imagine they were active in the Persian gulf... and naturally I'd imagine there are plenty of boats stuck in sand deep underground, undisturbed, and loaded with artifacts of trade.

[0]: http://people.rses.anu.edu.au/lambeck_k/pdf/171.pdf