Dry-shod

For much of the Ice Age, men walked dryshod on the bed of the North Sea many fathoms below where ships now sail.

And the Lord shall utterly destroy the tongue of the Egyptian sea; and with his mighty wind shall he shake his hand over the river, and shall smite it in the seven streams, and make men go over dryshod.

There, if you are in luck, you will find the tide out and the place fordable dryshod for a man on a horse.