I was sent this link by Galicia Máxica about the building of the dam that created the Belesar Reservoir.
.The video (in black and white) lasts only just over 5 minutes. Unfortunately, for me at least, the commentary is in Spanish, but you can get the gist of it. Seeing the old village half-submerged with the villagers looking on is very sad. You can see them erecting the church of San Nicolás with the numbered blocks.