I did this route after seeing this comment on Komoot about the boat (as an alternative to the main road into Mertola as I didn’t like all the lorries). I cycled down to the river and there was a man in a garden there, I asked him and he took me and my bike on a boat across the river (with his dog Snoopy) for €2.50. Also there was a cafe on the other side to get lunch 😊