Near Pontevedra a branch leaves the main Portuguese road, runs through the monastery of Armenteira and down the valley of the mills to the estuary at Vilanova de Arousa, and then goes to Santiago partly by boat. It is called the Variante Espiritual, and it is the only stretch of any route to Santiago normally travelled on water.
The reason is the translatio. In the legend, the body of the apostle was brought from Judaea by sea, entered the Ria de Arousa and was carried up the river Ulla to Padron, where the stone mooring post, the pedron, is kept under the altar of the parish church and gives the town its name. The boat leg follows that supposed course, and it passes a line of stone crosses set in the water along the estuary, the Via Crucis maritima, said to be the only maritime stations of the cross anywhere.
The variant is a modern reconstruction in its present form, promoted from around 2010 by local associations and municipalities, and it is honest to say so: the route existed as separate elements, the monastery, the mill path, the boat, and was assembled into a named alternative recently. That is the same thing the Camino as a whole underwent in the late twentieth century, on a smaller scale.
The rest of the Portuguese road divides at Porto between the central route inland through Barcelos and Ponte de Lima and the Caminho da Costa along the Atlantic. Both cross the Minho into Spain at Tui or, on the coastal line, by the ferry at Caminha, which is a second small water crossing and the reason some walkers claim the coastal route also breaks the rule that a Camino is walked.